These basic operations were then standardized in a specification called: Basic Linear Algebra Subprograms (BLAS).
Some standardization then came along, with the identification of 'kernels' (basic routines) that most linear algebra problems needed in order to be solved. I'm not an expert on the history, but apparently back then, everybody just rewrote his FORTRAN version with simple loops. Engineers have been solving these problems with computers since the early days. Matrix multiplication (together with Matrix-vector, vector-vector multiplication and many of the matrix decompositions) is (are) the most important problems in linear algebra.
This kind of question is recurring and should be answered more clearly than 'MATLAB uses highly optimized libraries' or 'MATLAB uses the MKL' for once on Stack Overflow.