I think there are probably several factors involved in your seeing fewer places that fill propane bottles. Economy of scale and cost make the exchange bottles a better option than the cost of equipment and training and personnel time to refill bottles. I think the larger type bottles installed in the rig permanent are much less common and not a very large part of the market.
When it comes to class A motorhomes, and even the mid range and higher fifth wheels, many are going to electric refrigerators and stoves now, although the non diesel powered rigs still seem to stick to Propane for heating beyond what the heat pump type AC units might provide. When we were shopping last year and asked about this and the reasoning behind it, every dealer we asked said the primary factor driving this was that dry camping and boondocking were something very few people buying these rigs were doing.