"One of our guiding principles in developing Microsoft Edge is that end users should never have to worry about which sites work in which browsers. This philosophy—”the Web should just work for everyone“—led to our choice to target the “interoperable intersection” of web APIs in our browser engineering."

Many sites already don't work correctly in Edge, IE11 nor Firefox - it's too late, these are minor browsers, used by a smaller fraction of end users. End users on on smartphones use 95% a WebKit originated based browser aka Chrome/Safari. Chrome and Safari are bigger than the rest on desktop.

Sites in 2017 are tested against Chrome and Safari by web developers.

http://gs.statcounter.com/browser-market-share/desktop/world...

http://gs.statcounter.com/browser-market-share/mobile/worldw...