I think it's the organised violence in particular this time.

But to your broader point, either AWS is a privately operated company or it's public infrastructure, I don't believe it can be both. There is absolutely nothing stopping the owners of Parler from running their own servers either.

I think you are right that they will move to more fringe parts of the web, but I think that is just how regular society works. A society holds some values, and if you don't hold those same values within a certain margin or actively work against them in this case (non-violence), that society pushes you to the fringes.