Pretty much every company I’ve been in or know of values a vertical trajectory instead of a horizontal one for its employees i.e becoming a manager nearly always means a faster salary progression than becoming an expert in one or multiple fields.
Why is expertise valued less?
People management is harder than it seems. Getting the people working for you to be happy and high performing is not hard but balancing those needs across a whole team becomes challenging. 5 people trying to coordinate a schedule is really tough - ask any gaming group about availability. A big 15 person team is more than 3 times as hard.
Leadership is also much harder to learn than experience. Experience is just surviving the ordeal and knowing how to get through it better. It’s persistence and observation as you solve the problems as they pop up.
Leadership is knowing who to talk to, how to appeal to a person, how to read social cues and pick up on unspoken behavior. A team member is equally capable of building the team as they are of poisoning the team. Good leaders can recognize talent and temperament that gels with the existing people. You’re effectively picking other peoples’ friends. (And not such good friends that no work gets done)
Experience can be taught. Leadership has to be learned.
And yet not everyone can become a nuclear engineer or rocket scientist, programm architect, lawyer and so on, so your “experience can be taught, leadership has to be learned” falls apart pretty quickly.
Leadership is not in anyway less then any other job that you can become an expert in. It is just focused on social sciences instead of engineering for example and both can be taught. It’s dumb to say that leadership is something special, its just that it is the more accessible of fields that have a high skill ceiling as it is present in pretty much every work environment.
Tldr, I think your end point is dumb, but I do agree that people management is hard and is definitely a skill. The best leaders are experts in their own right and it is just a matter of contextualising leadership as a skill you can become an expert in.