I have a FWC Fleet Flatbed and while I am happy with it, I would agree that there are things that could be done better. But, there HAVE been incremental updates over the years that have served them well. Their flatbed campers were essentially a market first in the US, and now several other manufacturers are following along. They have updated the interior finishes over time - I too felt that the fake wood and bear themed cushions looked like a 1970's tract ranch house, but the new silver spur interior is far more modern (even Ikea ish) and durable, similarly with the exterior finishes. However you will notice that they still sell the fake wood, bear print cushions and white corrugated siding, because apparently that is what many of their customers want.
On a technical note, they have also updated the infrastructure over time - going to PEX plumbing a number of years ago and now manifold based modular plumbing, from Dometic fridges to the more efficient Isotherm, from Zamp PWM solar to (unfortunately) the Overland solar branded Victron MPPT controllers, adopting LED lighting all around etc. Given their price point, I am guessing a lithium upgrade will be available soon. I really wish they would get rid of the junky Atwood furnace/water heater and switch to the Truma Combi, but maybe they will in the future.
Yes they could make the bodies out of a foam core composite, but when your entire manufacturing knowledge base is centered on welded Aluminum, there would have to be a VERY strong motivation to make the switch. I also wouldn't want to buy their first few years of foam core camper as it takes several years to work out the bugs. Without competition to push them to make drastic changes, there isn't much reason to make these changes. Currently there really isn't that competition.