Mostly for students in settings that may disallow either smartphones or calculators with specific advanced features (schools, SAT exams etc)

Also I don’t know about you but these days I welcome stuff that allows me to stay away from the damn phone.

I am pretty sure I could use a TI-89 Titanium in the dark even now

It's about ensuring "academic honesty" on exams. Also, it's nice to have buttons rather than a touchscreen. Also, there is something to be said about using a device with a different form-factor than the one on which a student also scrolls TikTok/IG and distracts themselves otherwise.

You don't. Most academic uses are now replaced by desmos, which is also used on the SAT. It's free, it's fast, and it does most of what you need.

i moved my ti-89 to be a phone app, but it was much much slower to type on the soft keyboard than it is to press the actual buttons.