[jimmy1]

Going to the bank costs something, if not the opportunity cost lost. When you are poor, every opportunity or cost matters much more. Most banks require some form of ID or address verification, which again could require travel somewhere. Finally, even if you assume the most seamless, easy to sign up online-only bank, you are assuming a stable, reliable way to access the internet, which again, can be issue if you are poor.

[Wowfunhappy]

Paying by cash has an opportunity cost too, over the course of doing it many times.

I think the bigger problem is that if your bank balance is (consistently) below a certain threshold, most banks will charge you a monthly fee.

[monocasa]

Before cashless stores, what was the opportunity cost of paying by cash?