There were claims on sandcars back in the day, and there still is.
But the volume of SxS claims is going through the roof. It all comes down to a profit/loss situation for insurance companies. With the sandcars, not that many people had them insured, because there really weren't that many out there...... hence less "market" for the insurance company... so all it took was a handfull of significant losses to make the program un-profitable.
now with SxS's.... the market share is huge... and most are financed (hence you should want to carry insurance), so the insurance companies finally have a market (hopeful profits) The problem is they are getting flooded by claims from the SxS programs... rates are going to the moon, and companies are limiting the amount of business they want from SxS. In CA, progressive has made it harder to write the programs, a few companies have already pulled completely out of the market... so in the near future, it will be similar to insuring a sandcar... (high premiums, low coverage, less options to choose)