What has NIL broken right now is that the money invested isn't necessarily tied to a return. In the NFL, if a player gets a media deal its because the business thinks they can make money off of that deal.
Not so with NIL. Usually they just want to get good players for their favorite team and hope that they win. How much money is a person/business willing to give just to see a team win? How long will that money last?
If you are getting positive financial return on your investment, then it can go on forever. But if it money goes down the drain just for the sake of winning, that won't last forever unless you are mega rich.