Considering how slow and unrespobsive big corporates usually are, there must be some real power broker behind it. Deplatformings usually all happen within the same day in a few hours. Last example is probably the deplatfoeming of Andrew Tate.
Some platform does a high profile ban, and then the PR inboxes of the other platforms are set ablaze with journalists asking for comment on how your particular platform wants to handle that person - high profile bans make nice clickbait articles after all - and the twitters and reddits and youtubers and so on of this world talk about what those other platforms are doing/are not doing/should be doing. At this point the other platforms have to do something, either issue a ban as well, or issue some kind of statement why at this time they won't be issuing a ban. Usually the option to just issue a ban as well is a lot easier and PR-wise "safe" than trying to come up with a "defensive" statement of why such a ban is not (yet) appropriate.
Google Groups aren’t as popular nowadays. My guess is a private Discord.