[Jensson]

Python is still slow today. I've worked with performance sensitive python at Google, there is no way to make it fast no matter what tool you use except to rewrite it in a lower level language.

Javascript is fast since it is such a simple language that is easy to optimize, more complex runtimes wont see nearly the same amount of gain from optimization efforts.

[johnnyanmac]

It's possible (Unity did it to C#, a magnitude more complex a language than Python), but at the same time we are not short on choices for other languages to extend upon. Google even made a few of those languages themselves.

There's just been no demand to make Python crazy fast, not to the scale where even Google will throw their engineers at it. Python's use cases aren't in real-time applications so that level of performance concern is simply not needed for many. And those that do will use anything else on the backend, from C to Go, maybe even Javascript.