Every time these american data plans are presented i laugh

look up at the skylines if you wonder where your money is going.
Unlimited 4g everything is about 17$ here
It's not black and white, you are comparing Apples and oranges.
The USA is much bigger than Denmark, hell, it's much bigger than Europe, so having all this (mobile) infrastructure is much more expensive.
There are a lot more providers in Europe than in the states.
These four providers here are the more expensive ones, you can get ones that are much cheaper than the 4 mentioned above.
I am also from Europe and if I get the more expensive ones I would pay >€50.
But, I myself have a prepaid one and are much cheaper off, guess you can find cheaper ones in the states as well.
We also had Neelie Smith Kroes the former European commissioner which started to make laws so that it's much cheaper to roam in Europe.
Mobile plans in the States might be more expensive but lots of other things are cheaper, for instance food, you pay a lot less tax in the States, and so on.