All these "industry changes" re tire pressure came about in reaction to the Ford Explorer tire fiasco, where Firestone took substantial blame for Ford's low-ball tire inflation recommendation. The same thing led to a federal requirement for a TPMS on every new passenger vehicle. About the same time, Toyo took a lot of heat over Toyo tire failures on Country Coach motorhomes, even though it was CC that had spec'ed under-sized tires. After that, Toyo refused to recommend any tire for a motorhome, regardless of brand.
With those two experiences in hand, the Tire & Rubber Manufacturers decided to place all future liability on the vehicle manufacturers. Then the RV manufacturer's lawyers quickly figured out that they must "recommend" for a worse case scenario to avoid any possibility of liability. And thus today they both refuse to acknowledge any other psi method or number.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL