Likely because they are a Java shop. All the IDEs they develop use Java, so they have quite an expertise in low level optimization for this language.
They also have C# expertise, but yes, Java is probably the language they have the most expertise in.
That's true, although, if you look at them, you wouldn't notice. The only mention of JVM you can see in the IDEs is in the About dialog, and the IDEs install and run their own OpenJDK, so no JVM has to be installed globally. Almost as if they were a bit self-conscious about using such an "unsexy" architecture...