I think the reason there are so many big rigs for sale is that there are a lot more of them sold new every year in comparison to Class B units and a gas Class A is cheaper to begin with. You can get into a new entry level Class A for less than a Class B on a Chevy or Ford and about half the price of a top end Sprinter conversion. Look at any dealer's lot that handles both and you will see rows of class A's and only a handful of Class B's and the amazing thing is that they sell all of those rows of A's to someone. I have had both and they both have their advantages. We purchased our last Class A to use for extended stays in Florida over the winters, we could not spend several months in a Class B. We now have another B, and it is as noted above, far superior for traveling and site seeing.
Nick