> these are distinct skills (people skills vs. technical skills)

I believe most people here will agree with that statement; nonetheless the problem is the ludicrous situation some people view the world through and consider that "junior techie moves to senior manager" as a fact of life†.

There is real social pressure on that front and lots of belittling of tech. Basically every time I meet some new person and say that I'm a software engineer, I get asked "But you still code at your age? Surely you'd rather manage people! What have you even achieved in life?" or any variation thereof and have to explain, justify even, that designing, planning, architecting, maintaining, and developing software is a real expertise domain in and of itself. The situation extends even in the workplace, where it is mostly expected of you to raise to management positions, and you won't get any raise if you don't "move past" "coding", as coding is largely considered a menial task by many, a sort of weird heritage of/transposition from an industrial culture.

† This has a vicious side effect of creating an ecosystem with mostly zero-quality software, since somehow only juniors and unskilled seniors code, because either skilled coders raise up the management hierarchy to get some raises, just leave for places/countries with a better mindset, or are overwhelmed by their unskilled peers.

You cant manage project on people skills alone. That just don't work all that well and is likely to lead to crappy product and massive crunch. You cant manage project without at least some technical skills. You don't need to know all details, but you need to know enough about tech to understand general concepts, what is possible, what is risky, what technical debt means, when people lie to you about tech. In order to be good project manager you need both, but you don't need to be super genius in either.

And there are also skills (or attributes) that makes you both better programmer and better manager: being organized, systematic, being responsible, willingness to do also boring tasks, understanding what people say when they talk to you, ability to explain yourself, good memory, etc.

That could be the reason for it. Mediocre engineer finds that they have a better head for managing people and schedules than lines of code. Either they talk to management, or management notices and offers the transfer.