That's a good point. However, in my opinion, what you describe only happens sometimes; it's what companies claim they do, but very often they don't. I've seen too many times (embarrassingly, including myself on some occasions) people promoted to a role they are incompetent in. I've seen an extremely solid staff engineer get promoted to principal, riddled with bullshit responsibilities, given a bad performance review when he didn't meet them, and quitting as a result. It absolutely happens, and often.