Boats are a specialty market, but how can you say that car and truck ads are unusual on radio, unless you mean advertising by the automakers themselves rather than dealers? Where I am now, car and truck dealers use radio heavily, especially country and AC.
Correct, the auto makers don't advertise on radio. Local dealers are advertising their dealerships and the services they provide. That means parts, repair, and used cars.
One of the biggest advertiser categories is auto parts. Dealers sell parts, as do car parts chains, such as AutoZone and O'Reilly. But those parts companies target primarily 25 to 54. Not a big category for 65+.