That seems to be the life-cycle of social forums online. The successful ones usually seem to have at least a slightly left-leaning user base, which inevitably attracts trolls/right-wingers/supremacists/etc. The trolls don't have much fun talking to each other, as they are insufferable people to begin with. It seems like a natural progression for them to seek out people they disagree with, since they have nothing else/better to do. Gab and the like are just the "safe spaces" they constantly berate everyone else for having (which they hate extra hard since their bullshit isn't accepted in those places)