Because Microsoft is not a reliable partner;

Just recently:

- they removed dotnet hotreload overnight for it to become gated behind a visual studio license

- they forced jetbrains to stop shipping the dotnet debugger in their IDE overnight, screwing their plan for their IDE Rider, they had to write a debugger from scratch

- their language server is still closed source and VS only

1. https://www.theregister.com/2021/10/22/microsoft_net_hot_rel...

2. https://blog.jetbrains.com/dotnet/2017/02/15/rider-eap-17-nu...