Numpy is most importantly BLAS and LAPACK, which can be implemented in any language. The best CPU version is probably still MKL, which is a mix of Fortran, C, and assembly. C is used for these kinds of projects because it is easy to sprinkle assembly into C.

Fortran solves a particular problem: produce a pretty good binary from readable code that a normal PHD student or engineer can write. This is not really the problem that a tuned BLAS/LAPACK library has to face, vendors throw very experienced folks at these libraries to chase after those last 5% performance boosts that Fortran leaves on the table.