The short answer
Because the ad slot and the answer are different products. OpenAI, Google, and other platforms state in their own documentation that ads are labeled placements around the answer — advertisers "have no ability to shape, rank, or alter" the answer itself (OpenAI Help Center, verified 2026-07-18). Ad exposure stops the moment you stop paying; presence inside the answer body persists after spend stops (it does require upkeep). And even if you do run ads, incrementality is the question: buying ads on queries where you're already cited means paying twice for reach you already have. That's why a citation baseline — measured across the places AI answers appear, by an independent third party that doesn't sell ads, with point-in-time evidence sealed at capture — is the data that should precede the ad decision, not replace it. Read the full analysis.
Why this matters
Buy the placement first and you pay again on questions that already carry your name. Without a baseline, that overlap never appears on the invoice.
Presence is sealed before any spend and read again under the same conditions afterwards, so the share the ads bought separates from what was already there.
Questions buyers read next
Where this answer comes from — Published pricesHow we measureTerms, defined