Maybe because they didn't use Git in their career or their role doesn't require to be hands-on. In my company, we use mercurial so I can imagine that some SWEs

Maybe because they didn't use Git in their career or their role doesn't require to be hands-on. In my company, we use mercurial so I can imagine that some SWEs aren't fluent in Git because they've used different tools. But apart from that, Git isn't rocket science. It takes a bit of practice like anything else but anybody should be able to know the basics in a few days, and become proficient after a few months of regular practice.