First of all, what most people call "the JVM" is really called Java. Java = libraries + VM + tools + language. Of the ~8 MLOC in the JDK, the Java language compiler and Javadoc make up around 200KLOC; the VM makes up about 1.5M. What is sometimes colloquially known as "the JVM" is really everything except the language, of which the actual JVM is pretty small.
Second, while the JDK is pretty modular (e.g. you can use the runtime and tools but not the frontend compiler as "JVM languages" do), we design every feature by looking at the platform as a whole. E.g. the relatively new records feature is implemented in the language, libraries, and VM. That's why some newer Java platform languages have more baggage than the Java language, because their features are not harmonious with the direction of the libraries and VM (e.g. Kotlin's coroutines and data classes).
Finally, it is true that back in the '90s, James Gosling set out Java's strategy to put most innovation in the runtime and keep the language very conservative (he called it "a wolf in sheep's clothing"), and we follow that strategy to this day, because it's turned out to be very successful. While there are lots of programmers who want more adventurous, feature-rich languages -- and many of them hang out here -- the vast majority of programmers don't. Many more people complain that the Java language is changing too quickly than changing too slowly. So it is thanks to the conservative language that the platform is so popular, which allows us to have the resources to innovate in the runtime.
So while <10% of people using Java do so with another language (no single alternative language has gained more than 5% of the platform's ecosystem) -- and we're happy we can accommodate everyone -- the conservative language is a necessary component of making the runtime state-of-the-art. A combination of an innovative runtime and a conservative platform is what most people want, and that combination is the main benefit.
