Performance. Firefox still lags in performance. Granted you may only see the difference in edge cases, but I work for a company that creates a performance-sensitive web-app and the difference is big.
I do agree however that the entire industry standardizing on Chrome is not great for anyone (including Google). I'm surprised that Microsoft isn't continuing Edge development, even only as a hedge and to have a sensible default for Windows - especially if you're building Windows Apps and you need a browser control. Why give that up to Chrome? And it isn't like Microsoft can't afford it - they are almost a trillion dollar company.
I do agree however that the entire industry standardizing on Chrome is not great for anyone (including Google). I'm surprised that Microsoft isn't continuing Edge development, even only as a hedge and to have a sensible default for Windows - especially if you're building Windows Apps and you need a browser control. Why give that up to Chrome? And it isn't like Microsoft can't afford it - they are almost a trillion dollar company.