Part of the reason solar is still a fringe thing for RVs is due to the costs up till now. Another big reason has been solar panel energy density; there simply wasn't enough room on the roof for the thousands of watts you need to generate for true full-time off-grid living with all the creature comforts (most notably air conditioning). Affordable, compact DC-powered refrigerators are still new (but are becoming standard items). Battery cost used to be prohibitive, and battery weight is still a problem. The 1200Ah I'm targeting (at minimum) is going to weigh a few hundred pounds.
If you want a residential-sized fridge, washer/dryer, and air conditioning that you can use 24/7, you need more like 3200W of solar and 2400Ah of battery. The larger the RV, the more expensive it is to cool. RVs have crap insulation, and most RVs are used in hotter southern areas. True self-sufficient electric and solar with no behavioral/comfort sacrifice still requires a lot of space and costs a lot.
The market is headed toward more solar, but the kind of setup you're talking about (and that I'm building for myself) is still quite expensive. And it's a huge cost for people that don't typically need it; the vast majority of people full-timing in RVs are content to do so at a sardine-packed RV park with full hookups. The market isn't going to bear the cost of massive solar installations as standard equipment.
