C# has a unique powerful position in the video game space. In almost every other niche, there are better (or just trendier) solutions, but C# is the only major language that actually gives you a combination of features that are important in video games:

- Dynamic runtime with loose coupling and hot reload of code - extremely useful during development.

- Value types. You don't want every Vector4 to be heap allocated when you're doing 3D graphics, because that's going to be absolutely unusable.

- Access to a relatively low-level substrate for basically-native performance when needed - extremely useful when you're trying to actually ship something that runs well.

Taken in isolation, C# isn't best in class for any of them, but no other language offers all three, especially not if you also want things like a really good debugger and great IDE tools.

To my knowledge, Java has none of these features (yet), and they aren't really important in a lot of the areas where Java is popular. But this is why C# in particular is very strong in the video games niche.