In my opinion, The value of programming "systems" like MATLAB lie in the fact that their primary customers are not really programmers but people like scientists and engineers who need to use computers and don't really want to (or have time to) learn new or better programming languages; These companies make their customers' lives easy by giving them easy to install and use, complete programming environments including a large set of domain-specific libraries.
I would add the very large old codebase in science. These systems gained popularity well before the advent of Python and other more user-friendly/approachable languages, so very large numbers of people in academia are familiar with them and have large volumes of code written for them.
As a grad student you're going to want to solve some problem, and your choice will be 1.) reimplement large segments of the lab's codebase in your language of choice or 2.) build something on top of the old code in Matlab.
I tried convincing my grad advisor to do things in python and not matlab, but no dice. He went with matlab for the problem he (and to as certain extent I) was trying to solve because of these kinds of institutional factors.
