It's more likely they never tried C#, but have a very strong negative bias towards it nevertheless. C# can also be written very functional if you want, it's a multi-paradigm language like Typescript itself.

Of course it _can_ be. But that's not how major libraries are structured. Which defines how majority of business apps are structured. The way majority of folks use a language defines the language in its entirety, doesn't matter if theres a kitchen sink of alternative paradigms. You can't argue that C# isn't enterprisey in the majority case. In JS you can build on top of a whole, extremely popular library ecosystem purely using functions and options objects.