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kotlinlang

I don't think that any syntax elements in Kotlin are somehow related to Java compatibility.

HotSpot can inline small / hot methods, but there are some work for him to do: load anonymous inner class, verify it, determine that method's code is small enough or hot enuogh for inlining, inline it. Kotlin allows to avoid all these manipulations so inline method can be compared with language constructs (e. g. Java's try-with-resources also does not generate anonymous inner class, it generates `finally` block's bytecode for you).
_(just for information: javac does not create anonymous inner classes for lambdas or method references for performance reasons, there are some mechanisms that allow treating a method as an interface implementation without creating a real class)_

Inlining without programmer's agreement clashes with Kotlin's idea that all things must be explicit.