A lot of web developers use a Mac to develop and test sites, but Edge doesn’t exist there, and it’s currently difficult to test Microsoft’s web rendering engine on a Mac without dual booting Windows. Microsoft is now bringing Edge to the Mac. We understand it’s not a move designed to grab more market share specifically; it’s more about making it easier for developers to test Edge. Microsoft hasn’t committed to a specific date for Edge on the Mac, but we expect to see it later next year.
I sort of get the argument here, and I’m not against more browsers on MacOS, but (at least for the foreseeable future) any websites that work in Chrome should also work in the built-on-Chromium Edge. You likely won’t need to test a site in both browsers because they’re—largely—using the same engine.
(Fun fact: it’s been 15 years since Microsoft stopped developing Internet Explorer for Mac.)