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?
Being a technical expert != being a good leader
There are a set of skills and attributes that enable one to leader well. An ideal leader will have both technical skills and leadership capability, but it is possible for each to exist independently in a person.