At its heart, brand bidding is a struggle over incrementality. Brands want affiliates to act as a “discovery engine,” finding new customers in the far corners of the web. When an affiliate bids on a brand’s own trademark, they aren’t discovering new customers; they are simply stepping in front of an existing one at the finish line and asking for a finders fee. For the brand, this transforms a partner into a competitor who is effectively taxing their most loyal traffic.