But the National Trust holds stuff in trust for the nation, and charges outrageous amounts for access to its holdings if you aren't a member (not to mention stupid opening hours at some of the more wildlife-friendly places.)
I believe members should obtain decent benefits for membership, but I don't believe that non-members should be ripped off. The RSPB actually charges fairly sensible amounts for non-members to visit its reserves. This is most likely why they don't think being scammed is a big issue, as for RSPB visitors its not worth the hassle of creating the cover.
The WWT and National Trust don't. The WWT has limited holdings and (possibly) either a problem with throughput meaning that they have to make their income from a known maximum number of visitors or a lack of belief that lower prices could attract sufficiently more.
The National Trust, I maintain, are a part of rip-off Britain. Their subs are high and their non-membership entry and parking charges are astronomical, which is why I haven't visited any of Britain's NT heritage sites in twenty-five years. Luckily, with that increasing distance, I've ceased to care about old buildings except for their potential as wildlife refuges. Knock it all down (or better, gut it all and let the bats have it.)
John