I would have expected them to wait with ads until OpenAI starts first and users switch to Gemini. Google is probably the player that could afford to wait the longest with this and increase their market share that way.
Actually I believe Google is the one caught between a rock and a hard place here because their stock will reprice once the market realizes how much their position has weakened re: search ads. They commanded an absurd premium on ads by virtue of being monopolistic leaders of search. They don't have a better product anymore, only a scale/distribution advantage.
They presumably were doing it to increase "engagement". More time spent getting infuriated with their worsening search meant more time seeing their ads.
They deserve to go under.
Meanwhile 1 minute unskippable ads on 30s YouTube videos, pop-ups on mobile that cover the video when you close an ad. I hope the UK TV ombudsman grows some balls and starts applying the law on advertising-to-tv-programming ratio. It needs to be applied when programs have ads in them too.