They build 300hp supercharged jet skis why not a sxs. And they are all over 1000cc.
Because the manufactures have not had their asses handed to them in law suits, and the manufactures have not yet paid for a law to be written to protect them.
Think about it. Why would these manufactures spend $100's of thousands of dollars to have ROHVA sponsor and pass a law that spacificlly put an engine displacement in the bill? They did it to protect themselves. I can assure you all the manufactures came together and chose what specs they were all willing to follow and have in the bill.
Comparing watercraft to utv's is like comparing apples & oranges.
Have you ever wondered why the Blm & the ISDRA do not require helmets on motorcycles, yet atv's & now utv's are required by law to wear them? Because both times helmet laws have been passed the manufactures were involved.