Life gets in the way for a while: Kids. Spouse/partner. House. Hobbies. Cynicism. Burnout. Health. Elder care. Then things settle. You work through the life thing, and in your 50's you get a fresh perspective and new energy.
I’ve had that surreal “we really want you to stay but we can’t give you a raise” conversation too many times in my career.
Then a subset of the gifted technical individuals grow tired of management, step down and go back to the tech to do what they really loved all along.
I've met a fair amount of brilliant engineers in their 40s/50s who have been through management and decided it's not for them and are now shining as engineers again after a decade lost to leadership roles