I think a lot of it involves the space provided. Around here, it's mostly a "Cruze In" where people bring what they have. No prizes or trophys. Just to show off. Here, the local WalMart offers a parking area on the side of their building. Nice area for showing off your ride.
Saturday, there was a $500 prize for best in show so take that small parking area and double the nuber of cars that normally show up and it becomes nothing more than a parking lot.