And yet there's Mathworks (MATLAB), Wolfram (Mathematica), SAS Institute, Kx Systems (q/kdb+), etc. Granted, these are all proprietary languages, but they aren't backed by the likes of Oracle or Google.
Exactly.
And even with things like Octave, SciPy, they still outperform them in ease of use, turn-key solutions in a lot of areas.
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.
If not for the plugins and IDE why would you use Matlab instead of Octave?
I don't know if this is true for the other languages you mention, since I have no experience with them.