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?
None of that is because of middle managers. No matter what, someone will need to job of coordinating with various departments, prioritizing tasks, selling ideas, motivating, and overall being good at coordinating. Idk if I’ve personally met a manager good at those things, but I know I would be worse at it.