Take things like SignalR for .net core, ServiceFabric, many microsoft server only products in Azure, (third party Akka.Net) don't support linux so well yet. Some of them are getting there but it's kind of risky to use due to the lack of being used in production for a while or it's lacking a feature or something is missing. It's been a while since the announcement of open source support, but it's seems like a slow process. It generally gives a vibe that they would rather have you use azure on windows, than support a completely open development ecosystem. They should put more weight behind the open source movement TBH. But it's an improvement, maybe they will get there one day. But right now I wouldn't choose it either for many things, considering the alternatives on linux. And last time I tried running code on linux and windows, the linux version was considerably slower for identical c# code. Might have been a missing compiler optimization, who knows. Not that I don't want C# on linux, I think it's a nice language in that family of languages. Like you said, it needs more success stories from running in a nix environment.
I realize you can use other databases, but once the data goes in, getting it out is a whole other ballgame.
As it stands right now, if your company is developing on .NET for the most part you are locking your developers out of the entire *nix ecosystem...from server licenses to command line tools to open source libraries to databases.
Combine that with how difficult Microsoft makes it to get your data out of SQL Server even for things like Elastic Search and you're in for a world of licensing hurt down the road.
I honestly still don't understand how anyone chooses a stack that locks you out of so many options and imposes so many constraints.
I get that Microsoft is improving...but they have a big hole to climb themselves out of.