Here's my theory - for what it's worth. And I base this on something the Mercedes-Benz Reps said during their presentation in Las Vegas at the first Leisure Rally in the USA (I am paraphrasing): "Frankly, we were taken by surprise at the use that American RV manufacturers have put these chassis to. We did not expect them to carry such large RV houses." They built them to be vans and trucks.
They were talking more about the reasons why certain components were never made beefier - the Sway Bar, as an example. And went on to say that, yes, they agreed with some of these modifications. Although, officially, the company tries to tell everyone they will not Warranty certain changes. One example of their shortsightedness is the fact that LTV (and the others) weld on (or have pre-welded) an extension to the chassis to accommodate the overall body length. This was one of the concerns of adding a Leveling System, based on some of my readings - would those welds hold?
Perhaps the choice or design of the chassis will change as Mercedes gets more involved in the design of their own RV fleet. Assuming they follow through with those plans. I do wonder if any of these companies have designed a chassis from the ground up for the express use of the typical 25-ft Class B+ designs. I would bet money that M-B thinks it is "silly" to offer any RV on their 3500 chassis with such limited weight capacity, as it is - but they just don't say that publicly. They seemed to really not understand the American Market in this regard. That may no longer be the case.