Think about it: if you have some Python application that's having performance issues you can either dig into a foreign codebase to see if you can find something to optimize (with no guarantee of result) and if you do get something done you'll have to get the patch upstream. And all that "only" for a 25% speedup.
Or you could rewrite your application in part or in full in Go, Rust, C++ or some other faster language to get a (probably) vastly bigger speedup without having to deal with third parties.