You are comparing two different things. BitcoinTalk was created by the one and only Satoshi to create a forum to share knowledge and to develop the bitcoin/blockchain technology which was at its first stages, while steemit was created much later after the cryptocurrency technology became a little more mature. While BitcoinTalk purpose is to share information only about cryptocurrencies and without any motives Steemit is a blogging and social networking website which means it's not only about bitcoin/blockchain/cryptocurrency subjects and the users are motivated to post to gain rewards and thus money so you can find a lot more of junk posts posted by people who only want to earn a few bucks.
Btw I love both sites I just think they can coexist togther