Actually, a lot of RV's have "real wood" cabinets. The door and drawer fronts are solid wood as are the framework. That real wood framework is however a cheaper grade of wood and is wrapped. Even our low end Wildcat was this way and could be considered "real wood". Below is a pic of our Arctic Fox.
You'll find very few trailers that use MDF/pressboard for the frames and they all use plywood for the body of the cabinet because it's much better than solid wood.
The back side of our cherry cabinets:
The biggest problem is people don't really know what quality is and aren't willing to pay for it anyway.