I think that failed because it appealed to a comparatively much smaller audience and that audience was likely more engaged with mainstream social media much more through amplifying other “leaders” content than creating their own. In a case like that it’s much more difficult to rapidly acquire the captive audience ready to jump ship to the new platform unless you can get a bunch of the most visible leaders to very quickly do the same before the outrage dies down.
In the case of Twitter these changes are impacting a much more diverse population of passive consumers and active content creators, and doing so in a way that these policy changes, if permanent, will induce chronic friction in using the platform, so it may be a better opportunity that prior movements to ditch existing platforms.
I’m talking about probabilities though, not predicting that as an outcome. And I think the overall probability, while higher, may still not be too high. But I’m just an interested observer with no particular expertise in the social dynamics of network effects, so take this comment in that context as well.