I HATE that career progression seems to require doing less of what you're good at and more of managing other people. Someone please explain how it makes sense.
So there is a lot of factors but I will be lazy and list out a few of them.
1. You hit a wall in your development -> Your growth eventually plateaus in so far as, any additional skill you earn is more and more niche and is therefore not as necessary. Therefore any resources spent on developing your skill set, rewards a smaller and smaller return. You are much better at what you do than anyone else, but what you do is limited.
2. Mentoring -> As you get older, you are not as capable of doing as much of the "grunt" work as you were when you started. This is simply due to age. Now theres no perfect cut off where your age offsets your experience, its a person to person thing, but rather than wait for that to happen, they want you to train the next generation while you still maintain your position and skillsets even though they become less used practically.
3. Higher Level Work -> Normally organizing, managing, delegating, and supervising is viewed as a higher level skillset. Its usually why those positions are paid more. Any company wants that to be the best person they have doing the work. Sadly, not everyone is a good leader or have those qualities.
This type of structure is fine as long as "those who don't have the qualities to be in a managerial position, are not in that position." However, ego from those who know the work but don't know how to lead, gets in the way. Beyond that,. we have those who have the leadership skills but none of the work experience. And finally we have the worst one, none of the work experience and none of the leadership skills but has the leadership position.