They are agreeing to make some money off of their Name, Image and likeness... now this is being used as a way for players to get paid, so to speak, under the table by boosters and such. But at the end of the day, if his Name, Image and Likeness isn't up to snuff where he is, he is most likely not getting a dime. Just because UNLV is 3-0 doesn't mean his NIL worth is worth more... it's still UNLV.
This is also a 2 way street as well... if someone agrees to pay him for his NIL and he doesn't own up to his end of the deal, does the company get to demand their money back because the athlete didn't meet their end of the deal?