Do you know of an ML language that's widely used in scientific computing? Julia was made to compete with R, Python, C++ and Fortran, combing high-performance with ease of use and general computing.
But mutability is also a great tool to have, for example for efficient dataframe handling and neural network weights.
>Procedural languages that are inherently distanced from math are used for math for whatever reason.
I think that historically it wasn't easy to make an efficient functional language. Numerical languages all trace back to Fortran after all (which is still alive and well). Nowadays, I think it's mostly because of inertia, and researchers having better things to do than learning a completely different programming language.