I think this happens because things that are going wrong are more interesting than things that are going well. (It's the old problem/solution problem; whenever you do a problem/solution ad, the problem ends up being more interesting than the solution.) It's also because nothing fundamental really changes in advertising. Have you read Murder Must Advertise? It's set in an advertising agency in the 30s and it's pretty recognisable to anyone who works in an agency now.
But working with new sorts of people in the past few years has helped me rediscover some of what can make advertising great. It was crystalised for me when a software guy and an experience designer were rhapsodising about advertising people's ability to be completely disconnected from the real world. (They meant this in a good way.)
Their example was simple - if Energizer or Duracell had a shop and advertising people were in charge of it, then you'd be served by a bunny. A real-life pink bunny. Your experience would be surprising, exciting, delightful. Whereas if Energizer really had a shop, it would probably just go for brisk and efficient (and it would maybe have a little model bunny on the counter). Advertising's genius is that it sells stuff by reframing reality, not by telling us about it.
Bruce Nussbaum of BusinessWeek came at it differently in a speech to the Royal College of Art: "Design is so popular today mostly because business sees design as connecting it to the consumer populace in a deep, fundamental and honest way ... If you are in the myth-making business, you don't need design. You need a great ad agency. But if you are in the authenticity and integrity business, then you have to think design."
Now, obviously, he's not trying to sell you any advertising here, and I think that he's got a point about the value of design and the need for authenticity, but he acknowledges what advertising does well: it makes myths, it tells big stories, it adds magic.
A great piece of advertising can change pop culture in the same way that a great piece of music or a great movie does, and that's a powerful commercial tool.
If only more brands tried to do that more often, tried to do the big, extraordinary thing, because even in a world of transparency and integrity, we'd still all love to hear some crazy, imaginative myths.