Sometimes a hotel is part of destination. We recently visited the Biltmore Estate and stayed at the Inn to enjoy the fine dining, although we camped at State Parks coming & going. Other times a campground might be a bit too far away to easily accommodate the schedule you have in mind. So there are reasons to do both.
A lot of the RV spending goes on a credit card that earns points toward hotel lodging, so the occasional free hotel room is (partially) another RV benefit.
EDIT: Granted it's easier to do "mixed" hotel/camping trips in a Class B. Parking is no problem.