My suspicion - for which I have no proof - is this: With search results, Google marks the ads. The marking has gotten ever more subtle over the years, but it's there. If you want to avoid clicking on ads, you can. With AI, Google wants to integrate ads seamlessly into the results. If you search for widgets, and Acme Corp. has paid Google enough, the AI summary will praise the virtues of Acme's widgets. And the user will have no idea that this is paid placement, instead of a summary of product reviews, etc..