Safety.
I've been watching some of those disaster TV shows. Very often some land racing vehicle has an absolutely disastrous accident, flipping and rolling and having a grand time. The same with hydroplanes.
In all those cases a cage protects the driver. Rarely is anyone killed.
I think those little cars can be made pretty safe. A few air bags, a cage-frame and whatever else they do and certainly one of my objections would be overcome. Actually, my only objection.
Arf