This is a fair point. It seems like standard policy at lots of places is to not budge significantly on comp unless a Valued Employee is prepared to leave. You then end up with one of the three scenarios:

- the employee leaves anyways, since it's too late to change their mind

- the employee stays, but there's a loss of trust and loyalty

- the employee never planned to leave in the first place, and exploited your broken system

Valued Employees should be rewarded preemptively.