I think part of the issue is the typical use pattern for RVs. In my storage lot there are numerous RVs which sit week after week with no usage. They could have been an impulse buy, or maybe they only intend to use it a couple weeks per year. It is just one of many facets of life, and maintenance is way down the priority scale.
Then take the typical construction of RVs. Fussy and maintenance intensive. I'm sure almost any RV could last a long long time with maintenance, rebuilds, whatever. But this isn't the typical ownership pattern to do that.
The typical owner would be well served by an RV with a roof designed to be relatively maintenance free, and building materials that don't rot easily. This type of production is not common, and would carry a cost premium.
Unfortunately many RVs are purchased for the qualities of big, flashy, and cheap. Ultimately this doesn't serve many owners well. Part of this is a manufacturing problem, part a consumer education problem. Perhaps expanding lemon law protections to RVs could be a small step in the right direction. Less incentive to manufacture clearly inferior designs or assembly practices. Consumers: Really research quality, and please make it an emphasis in your purchase decisions. It really is a more valuable commodity than big, flashy and cheap.