I would imagine since most things charge admission, like 99%, it's a fair question. In fact, I'm surprised the government DOESN'T charge. 😉
Because usually in these places people have to get a ticket to go in. But in USA places like this are for free. Another good example of that is Washington D.C where every museum is free ticket...
Maybe some people are not familiar with National Park Service attractions? They don't do their research before visiting.
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