The theory is that people don't want to click through blue links trying to find a source (or sources) they can trust, they rather want an instant summarised answer to any question. Google already does instant summarised answers for things like "when is the next public holiday" - generative AI content would expand these instant answers to any question, at the cost of accuracy. Google thinks ChatGPT is taking their market share (which it kinda is, and kinda was a year ago when they started developing this). The big idea of this new feature from Google is to retain market share, which is a prerequisite to making money.