Another reason that Internet ads don't completely supplant traditional mass marketing, is because a lot advertising is about creating a cultural consensus around a product. Beer is the classic example.

Corona wants to create the image that it's the beer for cool, relaxed dudes. We all know that there's nothing inherent to Corona that makes it the beer for cool, relaxed dudes. But through mass advertising they've created a widely shared cultural connotation for that brand. If I show up to a party with a six-pack of Corona, I'm projecting a clear message to everyone there that I'm a cool, relaxed dude. (Or at least style myself that way.) If I was going for sophisticated, adventure-lover I might show up with Dos Equis instead. And most everyone in America would understand.

For this type of marketing, hyper-targeted advertising defeats the purpose. You don't just want to reach the target customers. You want everyone in the broader culture to understand what your brand stands for. It's why mass reach advertising, like Super Bowl commercials or Times Square billboards command such hefty premiums. I watch a beer commercial at Super Bowl half time, and not only do I know that I've seen that commercial. but I know everybody else will too.