Probably incorrect conspiracy theory: with the success of Azure and also due to basic common sense, anyone inside MS that gives even the smallest shit about OS quality is a huge Linux fan. But, they have this awful legacy OS dragging them down, they can’t get rid of it because of various contracts and general shareholder expectations. They added as much Linux to it as they could really get away with, and their only good program (VSCode) has been ported and works perfectly fine on Linux, so things are mostly looking OK.
The only thing left to do is to tank Windows and get rid of that legacy support burden once and for all.
I think it's that, plus following where the money is coming from. While it's nigh-impossible to get retail customers to pay for windows and they want to get enterprise used to the idea of bringing everything into their 365 services, windows will be seen as a loss leader for other parts of the business, which includes advertising. Similarly I think google's purchase of doubleclick had a large influence over the years, android and chrome were in part ventures to present their ads.
The only thing left to do is to tank Windows and get rid of that legacy support burden once and for all.