My main concern with vendor lock-in in hosting (not just cloud), is that it'll easily turn business problems into ops problems. Credit card suspended because of (possibly spurious) "suspicious activity"? Cloud account suspended for non-payment. Trouble with hosting company x invoicing? Same result. Spurious DMCA takedown filed? Maybe a TOS violation - account suspended. Etc...

It's not so much that most of these would be permanent - but it does add risk of downtime from the "not ops domain" to the ops domain.

And multiple providers isn't a universal fix - but it might mitigate some risk.