Many motor vehicles are large dangerous multi-ton vehicles using a dangerously volatile fuel source. There's a reason we require extensive licensing. We need to ensure that only appropriately trained users are sold these dangerous devices. At about 43000 fatalities per year, they are one of the top causes of deaths in the US. You can't just let everyone operate machinery like that.

This is setting aside the scope for direct to consumer sales exploiting uninformed customers. Remember: safety regulations are written in blood.