The average for all USA cars seems to be around $2000/year, so even if FSD was half as dangerous Tesla would still be paying $1000/year equivalent (not sure how big insurance margins are, assuming nominal) per car.
Now, if legally the driver could avoid paying insurance for the few times they want/need to drive themselves (e.g. snow? Dunno what FSD supports atm) then it might make sense economically, but otherwise I don't think it would work out.