Could be that the mid-size appealed when full-size had terrible fuel economy, but now that mileage is up there's less reason to have less capability. Also don't forget that with the SUV craze of the late nineties and through the noughties, home garages got bigger on new construction to allow bigger trucks to fit. It may be that a true compact truck sized like the Ram-50 with car-like dimensions would make more sense than a mid-size that's too big yet not capable enough.