When I used to teach European students, they would invariably go out and buy the cheapest crap they could find like cases of pabst genuine draft and then complain how bad the American beer is.
I think the British equivalent would be if I bought a bottle of frosty jack and used it to declare all British cider to be shitty.
You gotta spend some money to get good American beer. Pretty much all the nationally brewed stuff is shit. There's a lot of local stuff that's actually good.
I'm not sure how European beer culture works, but one of the reasons to drink shitty American beer water is that you can drink it all day without dying.
One more useless fact: I long thought that adjuncts in shitty American beer like corn and rice were strictly cost cutting measures. There's definitely some truth to that. But the origins apparently go back to nineteenth century brewers being unable to achieve a clear lager with the barley that was available in America. When they used the barley exclusively, they kept getting a cloudy product.