People have reported a decrease in ROI from spending on Google ads already when they no longer control all the eyes and where you rank in what those eyes see when they search, that ROI will drop even more. People will stop paying for Google ads when the ROI is higher on other platforms.

Couple that with the fact that a lot of folks have moved their search to GPT or Claude once those platforms start taking in ad money... that budget will come from somewhere and that's likely existing Google ad buy dollars shifting.