Steemit rewards users with money. The idea is a "proof-of-brain" style network in which good content is rewarded and bad content is not. This hasn't really worked out, though, and if you look at the new posts section on steemit you'll see a mix of plagiarism, poor spelling and many people who've never heard of this thing called grammar. Clearly, this reward based system doesn't reward the good quality content.
Why? People want to make money, and they want to make money fast. Far from the steem whitepaper idea in which they claim that steemit is similar to a lottery – where a few people win, but everyone tries really hard with the belief that their content will be upvoted. Their idea might work, except that everyone thinks money and upvotes themselves.
Money might be a good incentive if it was given only when you post good content. But when you're given a list of posts to vote for, of which one is your own – are you really going to pick someone else's over your own?