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?
Broader reach and generally more responsibility.
I’m definitely on the “expertise” track at work and have specifically avoided management because it simply doesn’t mesh with my skillset or lifestyle. At my company at least, the people getting the calls late in the evening or over weekends are the managers. They are the ones that have to deal with scheduling conflicts, budget overruns, or fixing the big issues. They still take calls and deal with emails when they are on vacation.
While execs make a lot and probably don’t have the big stress, the juice isn’t worth the squeeze for middle management. They often don’t make that much more and IME are the most stressed group at a company.