It is for safety. Back in the day, when NASCAR was called "stock cars", the cars were based off cars produced for american streets. Cars designed for american streets have the steering wheel on the left. If cars went clockwise (turned right) the driver would be pinned against the wall, when they crashed in a turn. The old Riverside (California) road course had a long sweeping righthand turn with an outside wall. At full speed around that corner the drivers would be right against the wall.