I think you underestimate the downside and disruption here.
It's not merely letting people know so that they can decide their own stance. Taking down communications platforms as a strategy for communicating is much more actively shoving things into peoples' faces than you frame it... and also a bit absurd?
Anyway, the might as well stay on the platform that gives them more value. For so many that won't be Fediverse, and the disruption will have been just imposition and annoyance by people with an uninteresting cause to push.
@RedditGoneWild