They are pushing Linux hugely and one of its largest contributors.
Before the cloud you were spot on but they've realised windows can't compete in that area and actually costs them more when relating to their cloud services.
.Net is now open source and cross platform for exactly this reason.
WSL was created for exactly this reason as well and is awesome.
They won't create their own distro because, let's be honest, Linux isn't a competitor to windows as a desktop OS.