That's because advertisers like to spread their ads around. On TV, that's a good idea. Lots of people seeing your commercial translates into greater brand awareness. But you're not going to achieve that running the same, tired, old ad on every major Web site. To be successful, online ads need to follow the same rules as online content.
Online ads have to invite interaction.
They should be interesting in their own right. And they should be targeted at the audience of the Web site on which the ads are appearing. For example, imagine an online ad from a car company that included a query form right on the banner ad that let you search for cars in your price range. Or, imagine ordering something you needed, right from a banner ad, without having to click through six or seven more Web pages. Although banner ads will continue to dominate the Web scene for awhile, advertisers are also experimenting with new types of online ads, such as advertisements in the middle of Web pages, alongside them, or woven into Web page content.