That is what I mean by attractive; whether one path gets you ahead significantly better than the other. Otherwise people will flock to the attractive path, leading to a worse overall outcome for the organization.
It's a bit like making sure the characters in a game are balanced so the game "works".
I guess it depends on what you mean by "getting you ahead". It takes a mature and confident organization to implement this type of strategy for sure and allowing people, who are not managers, to make some of the strategic decisions.
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.
It's a bit like making sure the characters in a game are balanced so the game "works".