I suspect the reason is much more simple: it is more profitable for Microsoft to be platform agnostic. If that means supporting Linux, so be it. That does not

I suspect the reason is much more simple: it is more profitable for Microsoft to be platform agnostic. If that means supporting Linux, so be it. That does not mean they are going to abandon Windows, nor does it mean that they are going to reinvent Windows as a layer on top of Linux. It just means that they aren't picky about what their revenues are derived from.