Same as they can't do proper beer, cheese or gravy.
Really? Do you seriously think that you cannot get "proper" beer, cheese or gravy in the US?
From first hand experience over many years, I can tell you that you can.
As Doppler boy says, there are micro-breweries proliferating at a rate of knots here. Hundreds of different brews.
Vermont and Wisconsin have cows as far as the eye can see. Probably more cows in those two states than people. They make a bazillion different kinds of cheese, including mature Cheddar so sharp that it curls your toes. But not Stilton.
For gravy, you just have to ask for "brown gravy".
What we also have, is dogshit cheese, dogshit beer and dogshit white gravy freely available.
One shouldn't confuse "can't do" with "asked for the wrong thing because it's called something else".
Oh, and on the beer sizes.. most places that sell beer on tap will have two sizes of glass. 16fl oz and 22. The 22 is bigger than a UK pint. It just costs a bit more than the 16.