Because Windows can view and extract them out of the box without installing any additional applications. If it supported anything better out of the box I'd guess people would use that instead.
Subsume your agency. Stop writing. Stop learning. Stop thinking for yourself. Become hylic. Just let the machine think everything for you and act as it acts. Those that own them are benevolent and there will never be consequences.
I use one. I don't think that it would be a good substitute for this use case. You can try and do steno on your phone with Dotterel but it's not a good experience - you're better off using a swiping keyboard. I've not used a T9 system in my life, but I can imagine that it's a system that would let you input anything just typing with your thumbs. To have a good time doing steno, you have to exercise all of your fingers on both your hands. That's not quite so nice on your phone.