It's only anecdata but I'd highly question that. All companies I worked in (startup, midsize, megacorps) went with one cloud provider and stick to it. That is also not only my experience but also from friends who work in the same field. There might be a slight difference with megacorps where I saw them using multiple cloud providers but more like: Team A is using AWS, Team B is using GCP. But never: Team A is using AWS and has a copy running, ready to go, on GCP.

I tend to agree with the GP, to a degree. Chose an cloud provider and stick with it, the probability that the company changes the provider is very low (in the end all cloud provider offer the same with similar prices, no need to switch) but don't fully buy in. Like if you're on AWS, of course use RDS for DB and S3 for object storage but don't use Code Pipelines to build. So don't go "fully" proprietary.