Because it is not about buying things, it is about buying specific things. For example, buy potato chips - there are a number of brands (Lays, Utz, Wise, Cape Cod, etc.). Advertising puts their name in your brain and you base part of your decision to buy Lays instead of Utz based on the advertising image in your brain (beer and autos are other good examples). Companies cannot rely solely on brand loyalty nor random choice, and that is where advertising things comes in.
As for where they advertise (you reference web pages) - wee pages accept ads in order to keep their services free or low price. Same with magazines, newspapers, other media, etc. And ads are not "out of control" - you are seeing the same amount of ads now as you did when you were a kid, for some reason, they are registering more with you (advertising working).
So yes, Americans will buy - advertising is not trying to get you to buy generically, but they are trying to influence your choice when you make that decision to buy.