There is no need for MS to abandon Edge, especially when OS integration is going to be more important in the near future. Chrome and Firefox are also not as resource efficient on Windows, which his especially important on battery powered Windows devices. Same as on Mac OS, where you use Safari, if you value your battery life.
I imagine maintaining it is a big effort and keeping up an even bigger one. Sure they make billions, but still. What are they really getting out of this at this point.
Also there will be new mobile Windows devices very soon. https://www.windowscentral.com/upcoming-microsoft-hardware-w...