You might not believe it, but that is a fairly niche desire. There a tons of use cases for server software running only on server OSes (which these days, is some flavor unix 90+% of use cases)
And gee, Erlang is/was made to excel at server based software. Not desktop frontends.
My point C# can do 10 things. Erlang can do 1. If all you care about is the 1, then the other 9 C# can do are moot. If Erlang does that 1 better, then it is best (for that use case). C# is best for others.