You can keep arguing that “nobody left on that platform is going to be convinced of anything anymore,” but the fact of the matter is there are hundreds of millions of active users there, the vast majority of whom don’t give a shit about Musk, and aren’t as in-the-know about a lot of the current goings on that most Lemmy users whine about. As a politician trying to push progressive causes, AOC is on there for the same reason Musk is: it’s the platform with the most reach. It would be stupid of her to leave the platform. She has tons of followers, only a few of which would follow her to a different platform. It’s also the platform her opponents are on, and that’s the only place she can realistically call them out on their bullshit and her message be seen.