The JVM has simply has a lot more resources poured into it. C# and the CLR is a more modern clone of Java and it shines in the great usability of C# and to some extent the more sane op-codes of the CLR. Transforming between the two is actually easy enough that several projects offer 100% interop between C# and pure Java libraries.

I expect performance of the JVM to beat C# for a long time, but since the designs are so similar the difference isn't important in most cases.

Having spent time in both ecosystems, I'll admit that C# is easily a superior language to Java, honestly the best designed language I've ever used. Not surprising since it has the same designer as Delphi and Typescript. It's all syntactic sugar, but so much so that programming C# is significantly faster and easier.

What really hurts the .NET ecosystem right now is an insanely large gap in open source support. Something MS is fostering now but spent more than a decade trying to kill. This will not be easy to fix, as it's more a people problem than technical. MS actively tried to hurt the open source community for over a decade and to get support they will need to change the mind of countless people. It remains to be seen if this is viable.

If I was Microsoft I would remedy this by adding first-class support for Java libraries in C# by throwing their support behind existing projects to do so. This might close a gap that could otherwise take decades to fill