Julia Liuson promoted to President of the MSFT DevDiv, which now includes GitHub

How on Earth did you reach that conclusion? A trivial look at that list:

* Web browsers. -- Worked so well that IE remained the dominant browser for over a decade [1]. Of course, bundling was important here too but without the intentional incompatibilities between IE and Netscape, bundling alone would not have been nearly as effective.

* Office documents. -- Despite .docx files being notionally based on an open standard, to this day, Microsoft office will frequently reject as "corrupted" .docx files that have been edited using other implementations of the OOXML standard (in my experience, particularly when tracked changes are enabled or images are involved). In most such cases in my experience, the sentiment from coworkers is "why don't you just install Word" --- so apparently still working as intended.

* Instant messaging -- seems to have worked pretty well at the time [2] and remained popular for nearly a decade. And while they later lost marketshare to transformationally different technologies (texting, mobile messaging), the competitors against which they used the strategy remain dead.

* Against Java -- Led to major legal action, in which Microsoft was forced to pay Sun >$2B and agree to discontinue the practice in settlements, presumably only because by now people were catching on to the strategy. Failing that, Microsoft just made a separate competing language for cross-platform (AKA "write once run anywhere" :) development and called it.... .NET [3]

> And it's strictly better than Microsoft spending their time enhancing closed-source software, no? That was my question at the end: they could make .NET closed-source

Presumably it is reasonable to assume that they would like to grow the market share of .NET. While more open code is usually good, I would indeed not consider it "strictly better" if their goal in this work is to capture market share against other languages by leveraging the popularity and community that comes with "Open Source", while leaving them in a position where they can then reassert hegemonic control over their language via exactly the pathway being discussed here.

[1] https://en.wikipedia.org/wiki/Browser_wars#First_Browser_War...

[2] https://www.nplusonemag.com/issue-19/essays/chat-wars/

[3] The tagline on https://dotnet.microsoft.com is currently "Free. Cross-platform. Open source." The "Open Source" part of course only added somewhat more recently after the closed-source version failed to dethrone Java. Not that I like Java so much or anything, but you get the point.