How so?? JVM bytecode should be much easier to bind to, as the existence of JVM alternative runtimes for nearly every language shows.

Unless you're using a language that's specifically compile-to-jvm (e.g. Java, Kotlin or similar), almost nobody is using those JVM alternative runtimes. They're usually second-class runtimes that don't run the entire ecosystem of the target langauge. React Native runs JavaScript in a separate JS VM, Flutter is compiling Dart to native code with emdedded runtime, and Rust UI code also compiles to a native binary.

The "lingua franca" for language bindings is the C ABI which every other OS's platform libraries (Win32/Cocoa/GTK) support.