Legal tender

National parks are a treasure,  and now more people are starting to explore them (personally I've been to about a dozen, and hope to make it to many more in the future). 

But with the increased traffic comes a delay at entry because many of them have a small entrance fee. 

The park service decided to respond by making some of them cashless (though it's soon to be all of them). It speeds thing up when the rangers don't have to make change, they say. 

People have voiced their concerns and at times rangers have suggested that people simply go to a local Walmart and buy a gift card for cash and use that for entrance. 

But here's the thing that people point out: the NPS is a government agency. And they are saying this government agency will not accept the legal tender (ie dollars issued by the government).  There's something wrong with that. 

And then that begs the question: why is there a fee at all? The NPS gets a budget from the government. The fees are to cover the cost of vehicular traffic causing road wear and tear. They are nominal, but they exist. Why not increase the congressional budget by a few percent and remove the fee?