Making alternatives usable and getting actually good content there.
The most popular fediverse groups are:
1) (SJW-coded) far right containment internethatemachine echochamber
2-) mid-far left containment internethatemachine echochambers
... then after a while we start to find more neutral, less hateful options.
So long as the most advertized alternatives are vitriolic politics-based shitholes somehow managing to be more toxic than twitter and facebook, we're fucked.
Users are dependent. It's not illogical but its disgusting. Four years ago, we found that 97% of my uni cohort (USA) were facebook/messenger users. It's the opposite of herd immunity.
If you get enough people to use the alternative, it gets users (see whatsapp/signal/telegram). The initial launch is the hard part. Facebook committed reputational suicide over the past few years AND NEARLY NO-ONE LEFT. That's very important to understand.