There are two ways to look at this:
1. The park charges a flat nightly rate including the cost of amenities, etc.
2. The park charges a lower flat nightly rate and then charges a separate fee for amenities.
The benefit of #1 is that the park doesn't get questioned about the charge for the amenities by customers. The benefit of #2 is that they can publish a lower nightly rate in directories, etc., bringing in more customers. If a customer complains, they can "comp" them the amenities fee and get credit for their "good will" - but the majority of folks will pay and not say anything.
My personal opinion is that #2 is slightly underhanded and rewards the complainers. I get real tired of the "reward the complainers and unreasonable folks and screw over the folks who don't cause any trouble" practice of businesses. I would rather be charged more per night, the same as everyone else in the place, than deal with a company whose practice is to overcharge the customer unless they complain.