If you watch "Robots" most of those questions can be answered if you appllied that movie universe to cars. Also the Nascar style races are big because is what any car can do,but only a few are great at it, just like most sport in the real world, just because is the equivalent of an unpopular sport in our world, doesn't mean it has to be the same in fantasy universes, heck even in the same world they are different popular sports in each country and regions, In the USA you can see an stadium packed with 100 thousands fans for football, but here a regular football game is just the family of the players in the stands(if there any stands at all).