They didn't catch on.

I guess Octave's early adopters were the people who already used MATLAB or needed to use it.

Indian students did not, and still do not fit into either category.

Very few do the ML course on Coursera, and use Octave.

My own (non-Indian) experience is that teachers tend to have (use/d) Matlab, but then teach Octave / SciLab to students. (And it wasn't optional in none of the 4 courses I took that used it.)