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?
The company is not paying you for the amount of expertise. It is paying for how much money you will make them. If you limit your work to only what you can do yourself (without leading others), then you have deminishing returns. Only because I can now solve very complex problems because of my expertise, I cannot do 10x the work. Time is limited, expertise won’t bring you more of it. Leading will help other do their work better and faster, so you will be more valuable with that.