That may be the case for numerical code. However, a big niche for Python (if not the biggest one) is web services. How common is calling C++/Fortran code in a Django/Flask project? Those projects seem to have layers upon layers of pure Python code, with metaprogramming and whatnot.

Additionally, going through the FFI from C++ to Python and back to C++ has a cost. Eliminating this overhead was one of the motivations behind Julia.