Mathematica (and matlab for that matter) is effectively free at most national labs, and it’s still a tiny market share. That’s because scientific computing is rarely just scientists, but often includes engineers, SWEs, system admins, theorists, grad students, and more, solving lots of problems. If you can’t get wide adoption at a national lab, where are you going to get it?

Similar problem with Julia and Fortran even. They all have their niches and are great at certain problems, but Python (and C/C++) rule the overall landscape. in HEP, for example, it’s even the case that a full batteries-included C++ environment (ROOT) has slowly given way to python.