These brands are so well known, they are so ingrained in our culture,even if they stopped advertising, they would still be major brands.
Meanwhile these companies continue to spend millions upon millions on advertising.
I'm sure they are going after NEW YOUNG customers since most older consumers tend to be set on their brands and are not likely to switch outright to another no matter how many clever ads they see. Even still, if they are going after young consumers, don't these brands tends to be passed along through peers and family. In the case of these major brands I mentioned I just don't see how spending that much money is cost effective.