As you may know, Bing pays people cashback if they approach a retailer through a Bing link. So it's only natural that if I want to purchase something from, say, newegg, I will go first to Bing and click on a newegg link. That will appear to Microsoft as if their advertising were successful on me, while in reality I have already made my decision, and just take what Microsoft throws at me.
There are some retailers, such as ebay, that you have to perform a search before they offer cashback. So why not search for something.