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?
Leadership isn’t that hard to teach: find any band, raid group, DnD group or scout troop and you’ll have a high feedback learning environment for leaders and followers.
There are also several programs teaching a variety of leadership skills.
What’s difficult is that much business isn’t actually interested in leadership but productivity and control (management), yet conflate the terms.