It's a direct evolution of the search paradigm. You go from entering a few keywords roughly related to what you want and then clicking on ads to continue the se

It's a direct evolution of the search paradigm. You go from entering a few keywords roughly related to what you want and then clicking on ads to continue the search, to having a short conversation with the AI honing in precisely what you need and then having the AI complete the transaction or even generate the content for you, optionally with a transaction attached. The direct interactions with AI increase the fidelity of the customer model of you that Google has and uses to optimize sales to you for it's customers. Even further, the most common source of inspiration for purchases is the behavior of other people. If the AI can sufficiently emulate humans and ingratiate itself enough to you then it can directly influence your behavior just by suggesting that it would make certain decisions in your place or that others have already. This is actually not far removed from the existing situation, just the next level of technological capability. By actually generating responses for you, it starts training you to allow it to make decisions on your behalf. This may readily extend into purchase decisions.