Python is successful because everyone is aware that it has relatively terrible performance. As a result, anything remotely heavy is put into performant libraries that use not-python, leaving a nice glue language with fast libraries.
If you have something CPU bound, and it's python code hitting that ceiling, you're probably throwing away 10x performance [1]. That's ok, because anyone that cares about performance doesn't do that (or quickly learns).
Why would you rewrite something that already exists? It'd be a different story if the library evolved naturally starting with python, which it very much might if it was created today.
