Even in a language where writing three layers of loops is an okay choice (e.g., Fortran), I'd argue against using it everywhere because it is poor abstraction a

Even in a language where writing three layers of loops is an okay choice (e.g., Fortran), I'd argue against using it everywhere because it is poor abstraction and it will likely be less performant than calling the relevant BLAS routines. I believe the philosophy of NumPy is to outsource lower-level numerical operations to C. When NumPy isn't enough, one can always go to Cython or Numba.