There is often much more to a story than first appears. The park could have had several sites suddenly go out of service for any number of reasons. There could have been a flood, a collapse of a sewer line, a power failure etc. There could be a guest with a rig that had a mechanical failure and cannot leave as scheduled. Stuff happens.
Then there could have been a guest that flat refused to move. If the was the case, the options aren't exactly as clear cut as some people claim. Contrary to popular opinion, and perhaps common sense, the park cannot legally just call a tow truck and have them hauled out. A savvy squatter will know the law and the loopholes. They can claim a medical issue and the park (or hotel, where this is more common) cannot legally have them removed. As I have posted before, con men, grifters and thieves know the laws that apply to their activities better than lawyers. They know their way around loopholes and unlike decent humans they aren't afraid to exploit those loopholes for their advantage. It happens more than you know.