Actual harm caused by vendor lock-in with major public cloud providers, or such harm successfully avoided with a multi-cloud strategy, is like cow tipping. You can prove it doesn't happen because there's no videos of it on YouTube.

People talk a lot about their multi-cloud strategies, but I haven't seen anybody with a case study, "we didn't go multi-cloud and here's how it came back to bite us", or "here's how multi-cloud clearly saved our hide".

GitLab switched from Azure to GCP—but the lesson for them wasn't "we need to be prepared to do this again, so let's make everything multi-cloud". They went all-in on the new platform.