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?
They aren’t held back by the org that limits technical salaries and request that they take on leadership responsibilities?
An org that limits individual contributor salaries loses it’s individual contributors to companies that don’t. Senior principal engineers and principal engineers frequently make VP and Senior VP level salaries. If they aren’t, the talent leaves.
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.