I thought the whole point of them implementing it being open source was because MS was finding people were making library implementations better than them. Rainer Stropek in this video I thought did an excellent explanation of Microsoft's business model they're prepping for. They don't wanna be the one who deals with supporting your OS so much as they do wanting to be your cloud provider. Which is why they've been making strides in their implementations if asynchronous programming since the aim is most stuff is going to be on a VM.
I get the feeling the issue is that they haven't been able to bring their community along for the Open Source ride. The community it seems is looking for MS to guide them, rather then taking ownership of the ecosystem.
I don't know why, maybe it is that many .NET developers developed in an environment where MS provided blessed libraries for most things that was effectively bundled with the OS / Dev Tools licensing. Maybe it is that solid .NET developers end up working as consultants and thus have different vested interests. Maybe it is due to the size of organisations typically being larger and enterprisey.
Coming from the python / php / java / linux environments and dipping my toe into .NET in my current role, I believe the .NET ecosystem feels more different that any of the open source ones.
https://m.youtube.com/watch?v=Xv9Ho1UKsnM