I don't think NIL has a single thing to do with amateurism; instead it is about the ability to make money from one's recognition, like many others in our society do. NIL of each individual is a product, their own IP, and fungible.
The use of one's name, image, or likeness, has nothing to do with playing professionally or in an amateur fashion. It is not one's performance that is the product, it is their "NIL", simple and pure.
That is exactly why each deal is an individual business transaction between two parties, the NIL owner is not trading their skills performance for money, hence it has nothing to do with what level, league, etc. that one actually plays in. As a matter of fact, a great orator, a super influencer, a know-nothing popular figure, can do all the NIL they choose. Now athletes can too
The issue is that the size of the following of the place where someone gained notoriety is generally the important factor in NIL for athletes, the bigger the venue and stage of play, the more folks willing to anti up money for the use of one's NIL. This is why media coverage and population awareness is the key to NIL, and recruiting.
I know this sound Captain Obvious like, and it is. I merely say all this to try to stop the argument that NIL isn't fair or was a product of the big schools; it is a product of each person owning their own identity, and having the right to market that identity. .