The question is a bit more serious than it may seem. At first, one might think the question was, "Why do comedians joke about rape so much?" But that is not the question. The answer to that question is simple. Rape is a very serious topic and comedians take it as a challenge to trivialize and make fun of the worst most complex things in life as a way to make people feel less threatened by them. The other reason being that most of them never experience it as a real thing in their life - if they knew how serious it was in real life, they might not joke about it so much. Then there are the people that have experienced the worst of it and they have no feeling left - all they can do is talk about it.
The question that is being asked now is, "Why are so many comedians turning out to be rapists?" It's been happening for a while. Since before a lot of us were born. Rape has been happening since before any of us were born. But rape in the stand up comedy world seems to be more prevalent than ever. Just a few years ago, the Bill Cosby controversy began when he was called out on stage by another comedian, Hannibal Burress (See here: 
The craziest part of all of this - none of the people I've mentioned so far have been convicted of rape or sexual assault, being acquitted of all charges so far. Jimmy Savile died before his accusations came out. But is this all happening because powerful stars are unable to control their urges for lesser famous comics/actresses/fans? I don't think that's the only reason. Because we see sexual assault all the time in the lower levels of comedy as well. There was an instance of a lesser famous headliner somewhere in the mid United States that was accused of assaulting a female waitress at a club. No criminal charges were filed, which is why I couldn't call this sicko out by name. I just remember it being passed around the comedy community via facebook and seeing that he was still working other clubs even though people were passing this stuff around. There is the situation with DSI Comedy owner Zach Ward (see here: http://www.heraldsun.com/news/local/counties/orange-county/article159897244.html) who has now stepped down amongst allegations that he was "mistreating" female comedians/employees. There was Aaron Glaser of UCB theater in NYC who was running independent bar shows and stuff at UCB theater until 2016 even though people were accusing him of rape since 2010. UCB knew about rape allegations against someone working for them for 5 -6 years before doing anything about it. There was the owner of The Experimental Comedy Gallery in Brooklyn who raped an open mic comedian about a year after the venue opened. There are just so many rapists in comedy.
And among the several others that have been accused recently is Rebecca Rush. A female comedian being accused of raping another female comedian. The allegations are that she used fake profiles, told open mic female comics that she was the creator of a Comedy Festival, used a fake name possibly, got someone very drunk, had her way with her by inserting at least a finger (because there was allegedly a piece of a fingernail found in her vagina upon inspection), and then stole the victim's xanax before fleeing the scene. Now, let me start by saying that I don't know Rebecca very well. I've only had 3 interactions with her and I've seen her 5 times in person. First time, we did a show together and didn't speak - however, she was on stage calling out a comedy club owner/booker that I know personally for sexually assaulting her. The backstory to that is basically that they were dating and she says he tried to rape her in a bathroom when they broke up but she was able to fight him off - all heresy and no evidence plus no charges. I never stopped working with that guy because he books me, he's never done anything I would consider inappropriate in front of me, and I didn't know her well enough to know what to believe at the time. Now, at this point, I truly believe she was making it all up - but again I have no idea. Second time, we were talking in a circle and she acted like she didn't remember me from the show we did the week before - it seemed like she knew who I was and was clearly pretending. Then we did a show together that I hosted in which all the comedians take acid and/or mushrooms. Everyone gets pretty fucked up but it is an unforgettable experience. It's a packed show at the Creek and the Cave in NYC - and we usually have some special guests (past ones have included James Adomian as Bernie Sanders and TJ Miller as himself was on the show I'm currently describing.). Rebecca acted strangely toward me again at this show - before the show I explained that I wrote parody songs that had the performer's names in them and that I was going to use the songs to introduce each performer - she was like the 5th act so she'd seen me do it for 4 other people, she still acted like I never told her about it and had no idea what was going on. She had a very mediocre to okay set and we have video evidence to prove it. I mention that only because I've heard other people say that she goes around saying that she was the "only performer who could handle her drugs and had the best set on the show." BS. Then about a month later, I actually saw her standing outside the Experimental Comedy Rape Factory and I started having a conversation with her and some other person. We were smoking a joint. And then at some point it was just us. And she asks me, "Do I know you?" I was blown away. I walked away from her and the next times I saw her in the distance, I legitimately avoided her. She was clearly doing that to make me feel a certain way and I didn't like it. Then someone told me that she's an alcoholic and a pill popper and she probably really had no idea who I was. Either way, I don't want people like that in my life. Then my roommate was booked on one of her shows and she bumped him because he wouldn't sell her xanax. So do I have any idea if she's a rapist? No. Do I think she probably did whatever she is being accused of? Yes. But that is just my opinion. All I know is that she is clearly a shitty person and she comes off as a complete maniacal sociopath in this video where she talks about being accused (and in a lot of ways incriminates herself even more. Like when she says that someone who invited her to a nude beach wanted to be prayed on. You can decide for yourself. See here: 
There are so many comics that I've looked up to and when I hang out with them, I realize that they couldn't give one single shit about me or friendship - they are scoping out mates. I got to hang out with Joe List one time. Back when he was still drinking. Now he's sober. He was in Montreal headlining the Comedy Works back in 2012. After the Saturday late show, we were drinking and smoking weed and hanging out, can't remember how much of what he took part in. What I do remember is that he got hungry and wanted me to take him to the nearest McDonalds. In that McDonalds, Joe List hit on and verbally assaulted every single person (man or woman) to enter that McDonald's as he waited for his Big Mac. Now, I'm not saying Joe List is a bad person. He was actually really funny and cool and he didn't cross any lines of the law or even really any societal boundaries that night. Nobody in the McDonald's was angered by his actions. Most of the females he spoke to thought it was extremely funny. But he was definitely acting like a degenerate. A very funny degenerate. Had he gone just a bit further, and physically grabbed someone or blacked out and did something obscene - then I could see there being an issue. I would have been hanging out with a bad guy. It was that fine line, which he didn't cross, that made everything okay. He's doing very well in his career by the way and you should check out his podcast (See here: https://soundcloud.com/tuesdays_with_stories).
But all of this comes down to the point that comedians like to live on the edge and act like degenerates most of the time, and the rest of the comedy world is filled with hopeful dreamers that just want a little piece of stardom and will do anything to get it. This is a perfect mix of predators and prey. However, it's really only perfect for the predators. Most of the prey that do try to come forward with allegations against their rapists find themselves coming up empty handed at the ends of trials where everyone seems to be getting acquitted and the rest don't even bother because it is more of a hassle than it is productive. Some people feel like if they come forward with information like that against someone that is more famous than them that it will somehow hurt their career.
So what's the solution? There is really only one solution, at the individual level of course - in which you can just not be a creep and don't assault anyone. Keep up the good work if you've already been doing that. Comedians being respectful is not something that I see enough. But that doesn't fix the fact that you can't control other people and the entertainment industry, especially the comedy world, is a scary place full of creeps. I think more people should go to the police about assaults. I think more rapists should be punished for the awful things they put people through. The only thing tougher than being sexually assaulted has to be watching your assaulter achieve success and stardom while you get stuck doing open mics and bar shows.