How so? Microsoft want to support everything they can on Azure. That is just sensible business IMHO.
However there are businesses out there who like to work in a single vendor system as much as they can. I have no doubt that Microsoft will come out with their own Linux distro in the next 2-3 years. They don't need too, but they also didn't need to do lots of the things they have done recently.
Your argument is that Microsoft would introduce their own distro (a "proper" Microsoft Linux), and then declare their Linux-related ventures only "supported" on that Linux.
I feel like I've accidentally stumbled upon some internal discussion group of Microsoft's where very low level employees who completely misunderstand the market give their Microsoft-centric view of the world.
However there are businesses out there who like to work in a single vendor system as much as they can. I have no doubt that Microsoft will come out with their own Linux distro in the next 2-3 years. They don't need too, but they also didn't need to do lots of the things they have done recently.