If strictly hosting illegal content / being slow to remove it means you should be booted from AWS then how on earth is Twitter still using AWS?
They just didn't. There's a difference between being slow and just not doing it at all.
https://www.techradar.com/news/twitter-signs-up-aws-for-its-...
Regardless, from the sound of it Twitter was working with Amazon on this integration. This means Amazon knew Twitter was at least planning on migrating. If Amazon was serious about being consistent they should have told Twitter right there and then that they would not be allowed on AWS since they violate AWS' terms of services in the same way Parler does.