Both. People who are promoted to management because they are good individual contributors are often lacking in management skills (they turn from something they are good at to something they are bad at), and people who crave and hard pursue management positions rarely have management skills (always bad).

Frankly, I think we all have a bad manager inside of us, and the problem is that being put in a manager position exposes you to humanity-draining incentives that feed the bad manager parts of you, until it defines you. Higher compensation and promotions for focusing on costs and not quality, and short-term gains rather than long-term stability.

If you're unusually self-aware and smart, and put effort into grounding yourself, you may counteract it, but most people probably just float through life and let those incentives define them and their choices.

It's a feedback loop.

Upper management can't tell what good work is, and thus whomever is the most shameless in talking themselves up wins, unless they royally screw up in a way that can't be missed. If you have any shred of humility or nuance about your work, you are almost certainly not management material.

I have met like 3 or 4 people that I actually had respect for in management roles, but overwhelmingly they were there solely on an overinflated sense of self importance rather than substance.

It also attracts narcissistic people without empathy (and sadic people), a bit like the church attracts pedophiles. Not everyone is, but in the end it's too many (over 0).

Both. Whether you're considering empathy or competency.

Increased power—in pay or in authority—may be followed by decreased empathy (they turn bad). Conversely, dark triad traits have been linked with success like promotion to management (they were bad already). The research on this side has been criticized, mainly for methodology. I think the underlying idea makes intuitive sense.

On the competency side, there's the Peter Principle, originally satirical but subsequently researched. Good employees are promoted to a position of incompetence (they turn bad, or rather, are promoted until they are no longer good). Or, they were incompetent and promoted anyway to get them out of the way (they were bad).

And the mechanisms are not mutually exclusive. E.g., a good employee is promoted, they are bad as a manager, then entrench as their new authority leads to less empathy.

I think they get promoted to management because they're bad.

They're not going to promote the guy who knows what he's doing, because they need him to keep working in his current role. The guy who slacks off, bosses people around, and gets chummy with the boss though? Perfect candidate for promotion.