(Disclaimer: everything I say in this post is simply my opinion, and I have no proof of any of it)
I avoided ".Not" from the beginning. I thought MFC did whatever I needed for Windosws (and still think so), though I might consider re-writing my own TINY version of their framework for any future things.
From the article: I watched Microsoft kill an Open Source Project
I do not believe they are *KILLING* it, per se. Holding onto the reigns tightly might be more like it. They are quite used to having dominance over the ".Not" stuff and do not easily relinquish power nor control. They *FEAR* (the reason control freaks control) that their tech will proceed in a direction that they do not like, and therfore MUST wield a heavy hand. Frequently. At least, that's how *I* see it.
From their perspective, it's justifiable.
I think we can look more closely at WHY they made it open source in the first place: because of LINUX. And yet I do not see ".Not" on Linux being "a thing" (in any significant amount) any time soon.
How long has MONO been around? Yes, THAT long (15+ years). And the complaints were DEAFENING when Mono was suddenly part of gnome for Debian's package system, because of ONE application (that nobody used) called "Tomboy". Later it was (thankfully) REMOVED from the top-level package. I do not believe that there are ANY open source projects requiring Mono or ".Not core" (or whatever they're calling now) that are either ESSENTIAL or do NOT have native language equivalents (for example I use KeePassXC).
So, with the general 'need' to somehow "Embrace Extend Extinguish" Linux Desktops (and make them all like "WIndows II", as in the roman numeral 2, a hint to the retro flattiness and overly large controls, as Windows 2.x was), they need to steer the project in a direction that meets their "needs". Otherwise, they do not care if it fails. At least, that is how *I* see it.