Do you think that a sole source relationship carries an implied contract of continued service? Should that be a regulation? I don't think I'd like that.
As I understand it, AWS didn't force Parler to sole-source their computing infrastructure. And Parler claimed that they had prepared for such an eventuality.
I don't know if it would apply to the current situation with Parler, as my understanding is that they did agree to terms of service, and that the dispute with AWS over their content moderation didn't come up all of a sudden.
[0]: Certainly I think this in cases where you have a personal relationship with the customer/client, e.g. as a lawyer. It is less clear in the case where the service provided requires no real customer interaction as in AWS, where the services are all provided transparently, with no knowledge of who the customer is. But I don't want to get hung up on this issue.
That pressure would likely be successful.
But even if a datacenter is removed from one jurisdiction, Amazon is perfectly able to handle that loss immediately.