Because money! Seriously that's the answer to most of these questions.
I want the AI agent to act more like a fiduciary, an independent 3rd party acting in my best interest. I don't need an AI salesman interjecting itself into my life with compromised incentives.
(I mean, that could still steer it toward places that have affiliate programs, but if you're running a local AI tool to help you search for these things that seems like something you should reasonably be able to toggle on and off/configure in a system prompt/something.)
OpenAI was already taking steps to integrate ads, amd Grok shows how much we should be trusting AI as some impartial 3rd party. The goal was always about control and profiting off of said control. Pretty much the antithesis of hacker mindsets.