Because Google makes billions on selling ads on other sites through their DV360 / Google AdX products. Those ads need third-party cookies for targeting, otherwi

Because Google makes billions on selling ads on other sites through their DV360 / Google AdX products. Those ads need third-party cookies for targeting, otherwise the price drops by a factor 5. Google also happens to make the browser with by far the largest market share. So they're not going to axe third-party cookies as long as it drops their revenue 5x.