Most are of the "hot prospect" variety, and are being groomed for "the big show". NASCAR is following a "stick and ball" plan these days, they kind of like one trick ponies.
To give you some idea, when the old "Nascar North" tour went to the Bryar road course in the 80's, the 3rd fastest (after skilled roadracer Chuck Bown, and "wide open" Randy Lajoie"

, Dick McCabe was 3rd - his bait business made him haul dump trailers of wet fish guts from Nova Scotia to Kennebunkport, it was as if he had roadraced for years. There are similar stories about several truckers I know - Drive a non-synchro, 13 speed trans everyday, race cars are easy!