Why do Google, Bing and Yahoo allow search arbitrage?
Search engines run syndication programmes because partner sites extend the reach of their advertisers beyond the engine's own results page. Arbitrage publishers bring in extra searches the engine would not otherwise see. The engines tolerate the model as long as the traffic is real, the pages are honest and advertisers get acceptable value, and they tighten rules when it is not.
Search syndication is decades old. A search partner network lets a search engine sell more clicks to the same advertisers without building more of its own audience. Paying TAC to partners is simply the cost of that extra reach.
The tolerance is conditional, and since 2024 it has narrowed. Google retired AdSense for Domains as a surface for advertisers, tightened RSOC policies, and made the referrerAdCreative parameter mandatory so it can see what promise brought the visitor. Microsoft removed a number of publishers from its distribution marketplace in 2024. The pattern is consistent: engines keep syndication when it helps advertisers and cut it where conversion quality is poor.