

I don’t think vindictiveness is a major factor. This is about power.
Trump is trying to grab as much power to deport people as he can. He will fight every challenge to it until the legal options are exhausted. He will attack the legitimacy of the courts when he loses. He cares about the precedent and saving face with his base, not Garcia himself.
Some of them still exist; some of them shut down. It’s not just a matter of Reddit siphoning off all the users (though that’s a factor), but that administering and moderating forums is a lot of work without a lot of reward. In addition to the baseline effort being significant, a changing landscape including reduced organic search traffic, more spam, and increased legal liability in some jurisdictions has reduced the number of people who want to attempt it.
Reddit has many problems, but in my experience this is not one of them. Of course you’re very likely to be banned if you bring politics into a community that isn’t about politics.