I believe the reason they don't get NIL $ has income tax implications but this is just nonsense. He's getting paid.
They actually fleshed this out well in the article. It's not that foreign students are not allowed to get a NIL deal, it's that the terms of student visas prevent them from working in the US.
So what are the fixes? Well, I guess a NIL company could bring them in on a work visa. Since they'd no longer be on a student visa, then the prohibition against working would no longer be applicable. For what it's worth, the US isn't the only country to do this. I did a semester in the UK and my visa prevented me from working as well.
The second alternative, they also talked about in the article, that being that they can enter into NIL contracts so long as they don't actively work in the US. For example a company could post about a particular athlete on Twitter without ramifications, but the athlete couldn't retweet it.
Finally, and it was also mentioned to the article, when they go home they can promote the sponsor as much as they want because the "work" that they're doing won't take place in the US. Sanogo got a NIL deal with Sunoco when he was in college. They flew him out to the Bahamas and he was able to shoot an ad there.
So, there are workarounds.