It keeps you on there site. Same reason Twitter banned links and has grok now, the longer you stay on the site the more likely you are to look at or even click on an ad on that site. If you google something, then quickly scroll past the first couple ad links and click on the first non ad link you are maybe only staying on Google for 1 or 2 seconds. If you get an “ai overview” at the top and start reading through that then you’re maybe spending 10-30 seconds reading through that. That’s another 10 seconds that the ad was displayed that Google can go to there ad customers and say people were looking at it longer.