[microtonal]

In their hard drives, you can probably find Matlab, R, or (more recently) Julia files containing everything from implementations of Newton's method

This is a caricature at best. Lots of great, fast, commonly-used libraries for scientific computation are actually in C++. See e.g. Eigen, Blaze, Armadillo, MLPack, CGAL, Caffe, libsvm/liblinear,and GNU Scientific Library.

The ecosystem for such libraries in Haskell is currently (unfortunately) sparse. And in Python they are mostly wrappers around C and C++ code (apparently, Python programmers also like to dive in C or Cython when it needs to be fast).