Early German immigrant brewers in the US found that the available six-row barley produced a beer that was too heavy and protein-rich.
They discovered that adding cheaper, locally grown ingredients like rice and corn (maize) helped to lighten the body and create a cleaner, crisper product. 
These grains, called adjuncts, add fermentable sugars but contribute minimal flavor compared to malted barley. 
This results in a very neutral, light-bodied, and slightly corn- or grainy-sweet flavor profile, often described as mild or bland.
These beers are brewed to be highly attenuated, meaning most of the sugar is converted to alcohol and CO2.
This leaves a dry, crisp finish instead of a malty sweetness.
The bitterness (measured in IBU) and hop flavor/aroma are kept very low.
Hops are a relatively expensive ingredient, and a low level of bitterness contributes to a highly approachable and easy-drinking beer that won't offend a wide range of palates.
The best way to enjoy this beer is ice cold, which will refresh you on a long hot summer day. THAT'S ANOTHER REASON ITS NEARLY WATER!
The entire foundation of the mass-produced American lager industry - the segment that includes nearly all American adjunct lagers - was built by German immigrants.
It's not that you hate American beers, you just hate Germans!