boom nail hit on head, throw in bullying, malicious downvoting and not enough safety features (imho) and it doesn't exactly make it easy for new users, the retention rate reflects this, I think you sum it up best in your paragraph that says :
"Our recommendation systems are pretty bad. This is understandable. Steem has no AI, it's a blockchain. However, being proof of brain and all, we make no attempt to recommend things to people. We're very respectful of their space, and thus many, many users leave because there is "no interesting content", everything is mixed up in a very big unedible soup and each user is left to pick out what they want on their own."

While DPOS and proof of brain rule this place the big big crucial thing that's missing imho is proof of heart maybe