I'm not a lawyer, and I originally made a claim about sportsbetting covering a a subset of prediction markets, so just being covered for more laws that are not necessarily related to bets.

But I made some research, and here's the main body that specifically targets 'regulation' regulations for prediction markets https://www.cftc.gov/LawRegulation/index.htm

I can see the argument that they are piggybacking off a body of regulations that wasn't designed for this. I'm not an attorney, so I don't know if that holds, but even if it does, it's undeniable that there are enough parallels between commodity futures and prediction markets and that's why it's being used to regulate so far.

If you argue for more or more specific regulation, it's probably going to be a fork, not regulation from scratch.

And as mentioned in other comments, there's existing laws around the subject of bets themselves that mean that there already exist loads of regulations around these subjects, in the end they are just contracts, which is one of the main branches of law and has a huge body of law and jurisprudence, so either it's inaccurate to say they are unregulated, or it regulation means something much more specific that I'm unaware of.