Plenty of good reasons existed for that wariness, and if they are doing this now it's because it benefits MS in some way. Maybe they just got sick of maintaining it and figured they'd buy some goodwill.

I typed that before reading the article then saw this:

Microsoft maintains a modern fork of Mono runtime in the dotnet/runtime repo and has been progressively moving workloads to that fork. That work is now complete, and we recommend that active Mono users and maintainers of Mono-based app frameworks migrate to .NET which includes work from this fork.

Here you go Wine devs, we're cleaning our our garage, and by the way, we would really like folks to continue to be hooked to the MS teat of .net instead. Please keep maintaining this for us. Aren't we great?