They would go with 600 volt batteries if they thought they could get away with it. 16 gauge wiring throughout the car. A motor that uses a quarter of the copper at a quarter of the weight.
Factor this in...
Eight volt batteries are far less likely to be "borrowed" or "misappropriated". Take a gigantic golf course with several dozens of cars. Employees know golf car batteries enjoy a large market. Good batteries are likely to grow legs and walk off. Golf pros told me stories years ago about customers who came huffing and puffing into the clubhouse complaining that their cart would not go. By the time someone went out with a rope to get it, they found the seat tipped up and the batteries gone.
In sub zero F weather, I coupled a monster 8 volt battery to 3 7-D six volt jumper batteries. 2/0 jumper cables. When I hit the solenoid button (Diesel) those 855 cummins, and 3406 24-volt engines used to quiver and shimmy as they cranked. Can't do that now with onboard electronics.