Which is kind of a bummer - it'd have helped the standards based web to have an actual powerful entity maintain a distinct implementation. Firefox is on life-support and is basically taking code from Blink wholesale, and Webkit isn't really interested in making a browser thats particularly compliant to web standards.
MS's calculus was obvious - why spend insane amounts of engineering effort to make a browser engine that nobody uses - which is too bad, because if I remember correctly they were not too far behind Chrome in either perf or compatibility for a while.