All of those sites are toxic customers. Continuing to host them will draw the government's ire.
For Parler, the Jan 6 Committee would have inundated Amazon with subpoenas for internal documents and demanded testimony from executives. It's understandable why Parler was deplatformed so many times: because nobody likes government scrutiny. The risk is clearly greater than the reward.
I'm not saying that this was the right decision for society, but I understand where they're coming from, and these companies should be transparent about their motivations.
