There are several reasons why people are still on Facebook, even if it doesn't pay.

First, it is hard to make a change. A lot of the people on Facebook may be hesitant to leave one platform where they have relative success, despite not earning anything tangible, to venture into a new platform. 

Second, let's admit it. Steem and a lot of other blockchain-based social media sites are not really very popular. So, it's not so much a specific Steem problem, but a general cryptocurrency adoption issue. It's very possible that they have no idea that there is an alternative to Facebook. Also, there isn't really a lot of marketing going on for Steemit, and the few that I've seen marketing Steemit makes it look like a "get-rich-quick" platform, which may be turning off a lot of bloggers. 

Finally, I've seen some mainstream Youtubers and Social Media Influencers try and fail here at Steemit. Maybe because, while the idea is the same, Steemit and Facebook are both social media platforms, after all, the similarities end there. A lot of tactics that would work in Facebook just don't work here, so I feel like the few Facebook users who gave Steemit a try, then crashed and burned, and just went back to Facebook.