They aren't just cutting two top drivers for the hell of it. The drivers just don't have a truck to drive since the licensing for the names/likenesses were withdrawn.
Multiple Scooby trucks are actually smart when it comes to increasing money/interest. Scooby Doo is obviously very popular with kids and adults alike. It's the same reason there's multiple Grave Diggers, Max-D's, Mutts, El Toros, Mohawk Warriors, etc. They're popular.