My interpretation of "Microsoft <3 Open Source" is that MS has realized that their power in the tech industry is not dependent on their source code being a secret, and that in fact making your stuff open source makes you more popular and influential.

In my opinion, MS didn't really cede much power to the community when open-sourcing .NET, for example. It would still be incredibly painful for a company to unhook itself from Microsoft's version of .NET, and .NET is still influential for all the same reasons is was before, because of MS's position in the software industry. I think the move was just MS moving the framework into the current paradigm of software development. All(?) popular frameworks are open source these days: React, Electron, ... It just doesn't fit with the times to have .NET be closed source.

It think is interesting to think though about Google directly providing the source code base for its competitors, Edge and the other Chromium clones. Maybe the lasting message of US v. Microsoft was that if you open-source your software, you're less likely to be perceived as controlling. Or maybe your software simply becomes more influential if it's open source! Chrome being open source allows Google to be enormously influential as far as web standards go. It would probably be a lot less so if Chrome was closed source.