This is true. However there's a problem. Pretty early on these platforms realized that if they take a heavy handed approach to censorship it results in mass exodus. That's how reddit initially gained popularity years ago (mass exodus from digg). So they are careful now to ban in small increments instead. It makes it much harder to organize a move and keeps the outcry to a manageable minimum. This is why I think it's so important for every online community to have a bunker set up in advance. By the time you're being targeted by censorship it's already too late.