It may not be any more, but to most people in the Linux world it just smells, and that's enough. It's like asking why people don't drink box wine. It's just not cool.
A non-proprietary example of this is systemd and Wayland that Red Hat seems to be pushing. They are not really that bad on their own, but I expect many important downstream applications will eventually require systemd and Wayland. Locking out the BSDs.
It's about the motives
"it's open source"
"it now works on linux"
it all doesn't matter if they'll go after your ass if you dare build tooling with their debugger (jetbrains)
or when they want to remove a feature overnight to make it exclusive to visual studio windows and behind a paywall
https://github.com/dotnet/sdk/issues/22247
it's this kind of things that makes it hard to recommend it to people, and Microsoft can't be trusted
That is why things can go very toxic. Windows is not suitable for use, there is no concept of privacy and MS has shown many times it doesn't respect users ownership.
MS has a leadership problem. It should have made clear internally that the free cross-platform developer tooling should cover everything for 98% of the developer community. They could keep diagramming and other enterprise features as a paid offering.
On the other hand: There is no competition for modern .net + Avalonia UI for fast and sleek native cross-platform desktop applications. Maybe Java + JavaFX, but I don't know enough about its current state.
Here's a competitor: https://platform.uno/
https://www.codeproject.com/Articles/5366945/Multiplatform-X...
For at least ten years now I don't know why anyone would work with Microsoft unless they had no other option.