> First, it’s important to understand that managers are held to outcomes.
Respectfully, I disagree.
First, let me point out that when I say "popularity" I don't mean friends necessarily in the nepotism sense (in response to your later point). "Popularity" is a reductive term but still a relatively accurate one. What's really going on here is the intangible factors lead other around you to interpret the same set of facts charitably or not almost arbitrarily.
A big factor here is similarity in terms of demographic factors and background. This so often gets wrapped up "culture fit", which itself can be a euphemism for more problematic biases.
The example I like to give is this: a person may work on a project for a half that never ships. It may not even produce an MVP. Given this set of facts you will people who will say "we learned a lot and will take those learnings into future projects" all the way to "this team failed to deliver a prototype and as such we canned the project".
What's driving this are social factors.
Managers are subject to the same social forces that drive this interpretation. A given manager may get credit for dealing with reports that aren't necessarily bad enough to be exited but would otherwise be a headache for someone else in the org. Or that manager may be blamed for their team being perceived as low-performing even though they're given projects doomed to fail (eg under-resourced).
It's also worth noting that with any form of stack ranking or performance quotas, another factor that comes into play is horse-trading. That is, different managers are competing for a limited pool of ratings. You will find that a manager has decided someone should be promoted and that report will find themselves high on stack ranking as a result. There's an implicit quid pro quo here because other managers can get your support (as a manager) when one of their reports gets put up for promotion.
> Of course, if you believe your entire management chain to be incompetent
It's not competence. It's biases masquerading as objective determinations and an implicit over-reliance on social cues and factors all while managers have incentives that may come at the expense of those of their reports.