It allows them to scrap more data and push their web services. It also gives them leverage in web standards completion. The have a browser and user base that they can diverge from chrome.
With the revelations coming out due to the court cases. Microsoft might be (or at least aiming to) get a cut of Google revenue like apple gets for safari users. Google is probably very happy that edge (which is 99% chrome) is the default in most desktops.