Sports chassis and similar units becoming obsolete?

When I bought my 11 DRW RAM I noticed about that same time many MD Trucks were for sale. Talked to one guy and he said as soon as it was sold he was buying something similar to my truck. He was having a hard time selling it, he said as many like him were doing the same.

Fact was these guys that wanted to to tow a heavy RV like mine had to go MD. Now for example I tow my 24k Mobile Suites at and under my trucks SAE numbers. If my RV was a triple axle I could tow much heavier.