It's not always your choice. In my country, you're basically cut off from banking services if you don't own a smartphone. I lived without one for years and had to give in a couple of years ago (second hand but perfectly usable — thanks to LineageOS).

The pain was self-inflicted in my case, but some people simply don't have money for one (as there are lots of people living on 200-250 USD per month or even less — they have nothing left at the end of the month).