Alternative platforms always start with the people that aren't welcome in the old ones - Lemmy was literally originally made as a communist safespace:

Fuck the white supremacist Reddit admins, want me to set up a self hosted one for /r/communism?
Hey all, longtime Marxist-leninist, recorder of left audiobooks, and megathread shitposter here.
...
So I've spent the past few months working on a self hostable, federated, Reddit alternative called Lemmy, and it's pretty much ready to go. Unlike here we'd have ultimate control over all content, and would never have to self censor.
...
Raddle isn't an option obviously since it's run by this arch anti tankie scum, ziq.