[OJFord]

Not GP but isn't it obvious? Compensation, future prospects.

If managers are paid more you're putting a price on how much someone has to dislike managing people or prefer spending their time ICing for someone else. I don't think many people will pay much (in opportunity cost) for that.

And probably more significant than the initial bump for many is when they're looking for the next job elsewhere, and can say 'led a team of x many' vs. not.