Does GM allow their wheelbase stretched or reduced like Ford does? If not, maybe that is influential. I also seem to recall back in 2009 when GM dropped, Hummer, Saturn, and Pontiac, they also dropped the cut-away chassis motor home package, due to low production demand. I wonder if that is still the case.
The motor home package deletes some things like carpet and seats, and adds other things like power windows & door locks and chrome front grille work. There is a lot more to it but you get the idea.
I agree the GM/Chevy chassis is quite nice. I would prefer it over our Ford, but back in 2007 when we bought ours, the Ford was 9" shorter than the Chevy, and our RV outfitter didn't offer but only the Ford. The Ford E350 version of our
Phoenix Cruiser fit in our garage, but not the E450 for it stands 3" taller. Our rig clears our garage door opening by 1 to 2 inches. It's dang close when our rig is empty.