If you’re building something that a cloud provider might adopt or build their own, well, isn’t that risky regardless of the cloud provider element?
I know some companies avoid one provider or the other out of competitive concerns. That seems easily managed with contractual obligations.
Twitter has enabled some borderline illegal behavior, but the account holder has been the one at risk. I don’t think Twitter systematically allows illegal behavior like parler did.
https://aws.amazon.com/aup/: You may not use, or encourage, promote, facilitate or instruct others to use, the Services.. for any.. offensive use, or to transmit, store, display, distribute or otherwise make available content that is.. offensive.
What does offensive mean? Who defines it?
Does this sound libelous to you, and do you have evidence supporting this? Even AWS's response didn't allege Parler "systematically allowed illegal behavior".
If someone hosted an MP3 piracy site or torrent tracker or carding forum on AWS, it would likely terminated too, regardless of whether Amazon are ideologically against piracy.
If you're a big fish with powerfu rich users like Twitter, then vendor lock-in isn't a risk. If you're a small, inconsequential platform that can be smashed like a fly on the window, then you really need to care about such things.
Parler outright refused to delete posts calling for the mass killing of politicians, even when those posts were specifically pointed out to Parler by AWS. This is all detailed in court documents. AWS very patiently tried to prod Parler into following AWS's terms of service, but Parler refused. This is a very clear-cut matter and those suggesting otherwise are either trying to deceive or being misled.
Twitter also uses GCP, and Azure I’m sure. Their serving layer is not hosted by AWS though, and I’m reasonably certain AWS could not shut down Twitter immediately simply terminating their AWS account.