When I was studying for PMP, I remember there was even a term for this. Because you're good at one thing, it was expected that you would be good at something else as well, not taking into consideration that managing people is completely different from the domain they were an expert on. Of course, sometimes it helps to have some previous domain knowledge to be able to lead a specific team, but that doesn't mean it's automatic.

What companies really need to realise is that there should be different promotion tracks, and some of them are individualistic, i.e. being promoted as an expert in their field, rather than being promoted to have to manage people.