So here's the thing: it's called a contract. And of course the minute a player signs one, there is a chance that another person at his same position will be paid more. And there's a chance that this player will provide stellar value to the team. There's also a chance that the player will not be worth the contract. Contract language and the NFL Players agreement says what a team can and cannot do about that.
Players, however, who (like Hill) have decided they want more than the contract they agree to sit out, threaten that they won't play for the team again, and create problems that can upend a locker room. So refusing to honor the contract is the way some players try to get more. Teams, on the other hand, must honor contract terms or get sued.
Do you get to not make your car payment because you decide that you no longer like your car?
Do you get to not pay back your student loans because you decided that, as it turns out, an education at that price wasn't worth it?
Do you get to not pay your contractor because after your house is completed (as agreed) it wasn't how you thought it would be?
Or if you love your house, the contractor gets to charge you more because it was well done and gave you great value?
It's called morals and ethics and just because it's sports it doesn't change things. That's why it leaves a really bad taste in the mouths of some of us.