If I had to guess, its because Matlab looks a lot more like "traditional" programming and so is more approachable to engineers & scientists with a C/Fortran/Bas

If I had to guess, its because Matlab looks a lot more like "traditional" programming and so is more approachable to engineers & scientists with a C/Fortran/Basic background. I also think marketing plays a part. Matlab has effectively sold itself as the go-to language for mid-scale number crunching (i.e. scientific-type problems that are complex enough where performance could matter, but not so complex that you need careful performance tuning or a supercomputer.) Mathematica can achieve similar performance in those sorts of problems, but in my mind, Wolfram has been presenting Mathematica as more of an educational/casual tool for one-off tasks. I can't comment on cost or licensing offerings, but that could be a big factor as well.