Earlier quoted context omitted.
What came first, the chicken or the egg in your scenario? Did they stop doing great work because the rewards didn't match? Or did you stop matching because they stopped doing great work? Always hard to tell.
It's not hard to tell at all. You could just, wait for it, make the rewards match the expected great work and test that way.
Instead, most companies reward no one and wonder why the good ones leave or burn out ("weird, they don't contribute at the same level anymore").