There are several threads on the subject - most in the Technology Corner section of this forum.
There are multiple problems involved in setting up good WiFi for a campground.
One is that it takes a good bit of expertise to set up the various antennas and repeaters necessary to ensure good consistent coverage of a large physical area. It usually takes an expensive professional to do such a setup properly.
Another is that many RV parks don't have a very high bandwidth access portal to the internet. When 50 or 100 RVs try to connect at the same time - and RV park need to have a T-1 line or higher - something costing a couple hundred dollars per month. If the RV park is not located in a major metropolitan area - that may be impossible, no matter how much money the RV park owner is willing to spend.
The third big issue is how people use WiFi these days. A shared system like an RV park will not be setup for streaming movies, videos, music by dozens of people at the same time. They simply don't have the bandwidth available. So when a few people get on the WiFi system and start such high usage links - everyone else trying to get on either can't or has very poor speed.
Another thing. I never check my e-mail or do any serious on-line stuff over an open public system like a park WiFi. It is always over a secure connection such as my AT&T Phone or my Verizon MiFi.
The nice thing is that yesterday AT&T cut my data plan costs by 1/3 with their new lower rates to compete with T-Mobile's recent plans.