i have a hard time with this argument. on one hand what you say is true: C# is a strictly smaller community than java. OTOH that's true of pretty much any language, and yet python, ruby, elixir, swift, golang, etc. communities are healthy and vibrant.
if what you really mean is 'java people won't switch to C# anyway', then i agree, but C# isn't a really a language for them. it's a language for people who don't like and/or aren't forced to use java by their employers.
People who aren’t forced to use Java will choose Scala or other JVM langs, like Kotlin, Ceylon (a favorite of mine) or even Clojure.
C# the language is not exactly that exciting. I get it, it looks attractive next to Java, but it’s still a verbose, corporate-first, sort of thing. If anything, F# is much more competitive. Too bad it’s on CLR.
This has already devolved into opinion territory but I don't think you're giving C# enough credit.
I picked up F# relatively early in it's lifetime (2006ish?), back then there were many language features in F# that you just couldn't do in C#. The gap closed a lot when C# got LINQ, generics, and lambda/first-class functions (these are relatively old language features by now).
If I want to write in an quasi-functional-programming language style I can do it without having the language get in my way. I certainly wouldn't call it a "verbose, corporate-first" language, although the fact that it can be used for that is a bonus.
Don’t forget Rx. Not exactly language feature, but certainly a great contribution to come out of C#/.NET. And who knows if it would have happened without LINQ.
I like the language. Just not enough to use it over JVM. And I think most people feel the same way.
The problem with native desktop Java applications that although Swing is quite powerful, it requires developers to go through books like "Filthy Rich Clients"[0] to really take advantage of it. Which very few do.
To this day I still meet developers that aren't aware how to change the default L&F to native widgets, for example.
Whereas Windows Forms and WPF already provide a much easier out of the box experience, and have tooling like Blend available.
I am curious what the JavaFX sessions at JavaONE will cover.
if what you really mean is 'java people won't switch to C# anyway', then i agree, but C# isn't a really a language for them. it's a language for people who don't like and/or aren't forced to use java by their employers.