I agree with most of what the OP is saying. Walmart and RVers have a synergistic relationship. Walmart is close to a perfect RV retail operation. They're everywhere, they had wide variety from groceries to hardware. We always need something they carry. They're usually close to major highways. And many of them allow overnight parking.
I personally have a pretty good opinion of RV parks in general. I know what to expect and have not generally encountered grumpy proprietors-although it is clear they exist. If the Walmart was emptying four RV parks, I'm not sure what the parks could do about it. It sounds like the area was overbuilt with RV parks. No matter what the RV park charged, they could not offer a full retail store with just about everything. Successful RV parks probably have two attributes: Well run operations, and Location Location Location.