the difference is the level of control

X and Facebook are closed source, so you can't review them and they could be hiding stuff in their code or just do things people don't like and we can't revert

they also control the servers and don't let you self host, so they can make bad admin decisions and there's nothing we can do

and they also horde the content so you can't get it from somewhere else, which means you can't just leave and use a different platform (not easily at least)

over here if you don't like the devs then you don't need to donate to them, you don't need to use their instance, or we can fork their code, or even use an alternative (like Mbin vs Lemmy)