Their motivation is always ads. The ai response is longer and takes time to read so more time looking at their ads. If the answer is sufficient, you might not even click away to the search result.

AI is a potential huge bonanza to search sites, letting them suck up the ad revenue that used to goto the search results

They don't want to direct you to the thing you're searching for anymore because that means you're off their site quickly. Instead they want to provide themselves whatever it is you were searching for, so you will stay on their site and generate ad money. They don't care if their results are bad, because that just means you'll stick around longer, looking for an answer.

To make search more lucrative, they've enshitified it and went too far, but for a short time there were great quarterly resukts. Now they're slowly losing users. So they try AI to fix it up.

It's also a signal to the shareholders that they're implementing the latest buzzword, plus they're all worried AI will take off and they've missed that train.