It wasn't all that long ago that standard cabs were by far the most popular pickup. I have only owned one double cab in my life with know cab and a half.....
I suppose you can't walk onto a lot and get a Dodge 3500 with the 30k towing package either.
As I said, not all 1/2-3/4 or 1 ton rigs for sale are meant for towing as we know it. Some 1/2 tons ate rated for towing more weight than some 3500' s aka 1-tons, so one must be careful and know what he is looking for.
Example:
Ram 3500 SLT, 6.7 -liter, Mega cab, short bed, 4WD 3.42:1 axle, A/T, DRW Towing capacity 9,050lbs