I think the problem is mostly in design.
RVs are designed to be used a few times and then thrown away. This is very different from, for example, S&B houses which are designed to be used every day, for at least a few decades. (Before 1970, they were made to last 100 years or more.)
RVs are flimsy and leaky because they are designed by people who think of them as playthings. So what if it breaks or leaks? As long as it is lightweight and fast to build, it's fine.
There might be market for RVs that are built to be lived in. They would be expensive, and heavy. I would probably buy one.