It is good to read the reviews. One of two reasons cause Wally Worlds to deny overnight parking.
The most common is that the local municipality ends up banning overnight parking in order to get another source of income from unwary visitors. Same stuff as a lowered speed limit sign hidden behind bushes, but aimed at RV-ers.
The less common reasons is that the WM itself either has an issue of 18-wheelers or RVs overcrowding the parking lot, the WM is in a bad neighborhood, or the parking lot isn't owned by the WM, so they can't set the rules.