The regular rules could never apply to Trump because Trump is not a regular person. And, no, not even comparisons to foreign leaders are apt, because as silly as American exceptionalism is, the United States is still different than nearly every other country in the world. And, it’s not just the position he’s in (for the next few days anyway), but also Trump’s willingness to use his account to make pronouncements unlike pretty much any other world leader (or at least, world leader of consequence).
Trump is, perhaps, the perfect example of why demanding clear rules on social media and how they moderate is stupid.
As for the question of why now? Well, clearly, the context has changed. The context is that Trump inspired a mob of goons to invade the Capitol building this week, and there remain legitimate threats that his cultish followers will continue to do significant damage. Certainly some people have insisted that this kind of violence was always a risk — and it was. But it had not actually erupted to this level in this fashion. Again, we’re talking about context. There’s always more context.