There could be an opposite avenue: ad-free Google Premium subscription with AI chat as a crown jewel. An ultimate opportunity to diversify from ad revenue.
The low operating margin of serving a GPT-4 scale model sounds like a compelling explanation for why Google stayed out of it.
But then why did Microsoft put its money behind it? Alphabet's revenue is around $300bn, and Microsoft's is around $210bn which is lower but it is the same order of magnitude.
Especially because the people who'd pay for Premium tend to be the most prized people from an advertiser perspective.
And most people won't pay, under any circumstances, but they will click on ads which make Google money.