My guess? The Python and Ruby developers have never shown any great interest in performance. Javascript performance only become recently popular.
EDIT: I should clarify that "Python and Ruby developers" is meant to mean the language implementers, not ordinary users. And this isn't intended to be a dig at those languages--only that they clearly have different goals for their languages than implementors of Java, Go, C++, etc.
EDIT: I should clarify that "Python and Ruby developers" is meant to mean the language implementers, not ordinary users. And this isn't intended to be a dig at those languages--only that they clearly have different goals for their languages than implementors of Java, Go, C++, etc.