In a way, it sucks that they do that. But from their perspective though, it surely feels nice and I bet many of us would do the same if they had the chance or the determination to build such a plugin or something similar.
On the other hand, for me for example, steempress' plugin is a good start, as sometimes, the biggest vote on my posts is theirs, which makes me still want to use it despite that cut - which from what I know, is 15%.
I've noticed other apps or interfaces that take their cut and stopped using them if they didn't bring any other value. But so far it's been a good boost. Maybe later, if my account grows, I won't need that anymore, but for starters like me it feels like a good enough compromise.
Also, from what I know from other bloggers who use Patreon or things like that, donations aren't really consistent. And I guess this gets us pack to the first point. Most people would take a bigger share for themselves if they could. I guess history has proven that many times so far.
Cheers, and keep on rolling, man. ;)
P.S.: Forgot to mention their curation rewards, which almost doubles their fee.
RE: My 2 reasons why I am not gonna put Steempress on my website.(warning: a little bit of rant)