I came across this article about the idea of migrating Parler, and while I can’t vouch for the source, nor do I have experience with AWS specifically, this generally tracks with what I do know about cloud infrastructure.
Basically, even if you find somebody willing to host, you’re looking at re-building every part of internet infrastructure from scratch (down to the data center level), for a product that might not even still be relevant in 6-12 months as their moment passes. Basically, you’re talking about building a 2020 scale web application with 2000 era capabilities.
It’s possible there are vendors for some of all of the services in e.g. Russia or China (AFAIK, China’s Great Firewall stuff means that it’s difficult for regular cloud providers to function there, so they have a lot of their own parallel infra built), but even if there was feature parity and you could find providers for everything you need, it would still be a major undertaking.
tl;dr: AWS provides an incredible amount of value, de-platforming works