I suspect that a lot of the impediment to JITing Ruby and Python effectively was due to large and important libraries (standard and third-party) being written in C using interfaces that were not JIT-friendly. JavaScript in the browser also depends on C/C++ interfaces to important functionality, but the entire stack for each engine was controlled by a single organization, and was always released as a unit (the web browser). I think this largely eliminated library inertia (or whatever you want to call it) as a problem when replacing a JavaScript engine.

The other advantage JavaScript had was that there were large, well-funded organizations (notably Google and Mozilla) competing on performance. Python and Ruby were always community projects and they had a strong emphasis on maintaining backwards compatibility with a large and diverse ecosystem, and there wasn't a lot of demand for faster implementations.

JavaScript is a relatively small and simple language with relatively constrained semantics that allow it to be implemented relatively simply.

Ruby and Python are the opposite of that. Ruby and Python are I'd say literally a thousand times more complicated to compile than JavaScript.