>Why not *just* move to C++ or something new...?

Moving to a different language is never a "just" in any non-trivial organization. With Python you have the option but not the obligation to optimize: you can write slow pythonic code or faster framework-y code. You also have the option to write python extensions in whatever language you want for performance critical parts of the code. The latter seems like a much more pragmatic aproach to me than completely switching languages.