It has been over 20 years but it was something we studied in an insurance class. I believe they considered it in California.I can see the insurance companies having a big fit over that since it would come down to only one carrier and the state would have to go thru a bidding process to see who would get the contract for the year and the pricing would be locked for a year so no surprise price increasing when they wanted to.
I did some DDG searching and this is what I found if anyone is interested:
There are other resources too, this looked the most detailed. Disclosure - I did not read the link, just skimmed a few pages.