The thought is, that people who search for a particular brand already have intent to buy an item, so adveritsing is preaching to the choir. I’d also suggest that social recommendations have lost their lustre as apps regularly automate this process on other’s behalf. Once advertisers realise this, platforms will need to crank up the screen space (see current Google search results or Facebook News Feed being cramped with ads), or more cleverly target you (see Axciom).
Then there’s always the risk of XSS in the odd ad here and there to spice things up.
“But in a study of search ads bought by eBay, the most frequent Internet users—who see the vast majority of ads; and spend the most money online—weren’t any more likely to buy stuff from eBay after seeing search ads. The study concluded that paid-search spending was ironically concentrated on the very people who were going to buy stuff on eBay, anyway. “More frequent users whose purchasing behavior is not influenced by ads account for most of the advertising expenses, resulting in average returns that are negative,” the researchers concluded.”