It’s also much easier to get promoted as a manager M1 to M2 vs senior engineer to staff engineer. Managers automatically have a lot of impact across multiple teams, but it’s much harder for senior engineers to demonstrate that.
On the other hand, I've worked hard to get IC's on my teams promoted up and out of my team because good directors rely on their Sr. Staff/Prinicpal engineers so there's room for them to grow (even if it's difficult).