Original link: Microsoft Offloads The Mono Project To Wine / Phoronix.
When Microsoft bougth Xamarin they also acquired the Mono project - the original open source .NET.
But since .NET 5 then Microsofts .NET has been open source (under MIT license), so they had obviously no use for Mono any more.
So they gave Mono to Wine.
Mono supports two platforms that .NET does not: AIX and i. But I guess legacy IBM platforms are not a priority at Microsoft. No surprise in that.