This of course brings up the highly controversial issue of whether you should optimize your architecture for multicloud or go all-in on one provider.
Edit: I would recommend Corey Quinn's thread for more background, but tl;dr it's hard to get kicked off AWS and it's not happening due to political slant
Parler should have known this was a risk going in. Being able to switch cloud providers is important if there is potential for controversy for your service.
From what Corey Quinn is saying, they have to be doing something really, really bad to get kicked off AWS, and no other host would abide it. Self-hosting wouldn't help them either, since their ISP could just yank the plug for the same reasons.
For reference, AWS hosts The National Enquirer, which threatened to leak, er, extremely sensitive photos of Jeff Bezos.
Edit: I would recommend Corey Quinn's thread for more background, but tl;dr it's hard to get kicked off AWS and it's not happening due to political slant
https://twitter.com/QuinnyPig/status/1348130385411018752