Two things can be true at once: my employee can be delivering good results, and my employee can deliver even better results. Just because an employee is delivering results doesn't mean that is their maximum potential.
The other thing you're not considering is the fact that management has a responsibility to maximize productivity with the workforce they have. Where you see management failure, I see managements responsibility.
Now, none of this means there aren't poor managers (I've had those), nor does it mean that the solution is straight up surveillance. What I am saying is as someone who does manage, and as someone who does pay employees, this issue isn't nearly as cut-and-dry as you're making it out to be.