Most colleagues did nothing of the sort and were roughly as productive without developing any broader skills, as far as any performance evaluations showed. It's spending an hour performing repetitive manual changes to some code, or spending 55 minutes doing it programatically in Vim and gaining some precious Vim-fu in the process. The output is the same at the end but the programmer isn't.
When there is no further scope to learn from my work (apart from pipe dream re-write projects that never materialise) and I am not doing any significant critical or analytical thinking, I leave. It sounds like your place had a lot more to teach you.
At least, I'm telling myself it's valuable experience so I can stick it out for the next six months.