They may have changed course but open source software has for 10+ years largely avoided the platform. This means C# is Java with nicer syntax but 10% the libraries and terrible cross platform support.
There's been countless times at work when I needed a certain library and I already knew what the Java equivalent was, but what I was looking for simply didn't exist. Database clients, data processing, http2, image manipulation, etc...
With Java I get everything I do from C# plus all the stuff they've been raving about working on in .NET core . Plus I get choice. There's 3 full featured IDE's, 20 or so servers, 6 or 7 JVM's