Bingo! There isn't a cloud OS and then an standards-ish implementation of that standard. All of the clouds are bespoke and closed source. That said, nothing weird about needing specific knowledge for running on the specific thing.

If I run a motorpool that is all Prius, then I'll want Prius mechanics.

At some point, I think I hoped that Kubernetes would be that "cloud OS" but as time passes, I'm not sure that's going to happen and I continue to make sure I stay abreast of the various closed source cloud ecosystems, including AWS which has served me reliably for over a decade.

Windows Admin vs OS Admin then.

So if it's owned by a single company you can't list it as a skill? Huh?