Here’s a blog post I made recently showing some fun SymPy calculations. https://www.swied.com/posts/make-a-ringtone-sound/make-a-rin...
I think the free-ness of Python is a really big deal, because free means you use it for everything, and you use it for things that you expect to share. I don't know the present license terms of those programs, but it used to be that unless you worked for a really enlightened organization, if you had a seat of Mathematica, it meant you had exactly one seat, probably on the computer in your office, possibly the only seat in your department. If you also had computers in the lab, at home, etc., those computers were running something else, such as Python.
If Python ever got good enough at something previously reserved for commercial software, even without being comprehensive at that thing, it triggered a decision on whether it was worth the headache of maintaining the commercial license and being chained down to a single computer.
I don't do large math projects, and have been satisfied with Maxima. Where I'm beginning to use SymPy is to contain the derivations for formulas within the same Python code that uses those formulas. Mainly it's a readability and documentation play.
I left matlab behind years ago, but I still use mathematica occasionally.
Though I haven't made a serious effort to try out Maxima, Reduce, or Sagemath.