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?
Because bosses always want to make more money than the people they’re bossing. But, also because leadership is responsible, I (engineer) wouldn’t want to take the responsibilities of my boss for the same pay.