I was in a park with similar rules and their explanation was that your router/amp/ranger extender must use one of the limited number of channels available on the WiFi Networks (Channels 1-11) and would cause interference with their networks so none of these devices were allow. This included WiFi type devices as they also use the same channels to broadcast a connection to the devices inside your coach.
The RV park has every right do exclude anything they like (i.e. we reserve the right to refuse service to anyone for any reason).
Failure to abide by the park rules would lead to eviction and that particular rule was very well advertised in the office as well as with yard signs throughout the park.