"the only reason I'm still on Reddit is that there aren't any alternatives"

To add to your point, I only found out about the fediverse because a couple of the subreddits I was active in made a post declaring that they were going to move (or at least start up another version of itself) in the fediverse. I'm currently still on Reddit because I'm not seeing enough content, and the federation seems really hit and miss, to serve as a sufficient alternative.

Until you've got a critical mass here, I think it'll be necessary to use reddit itself to help raise awareness