Forget banks, many don't have ID. Ration cards exist, but those are tied to your household so you may not easily be able to get access to your ration card (say if you're in a city with family -- and ration card -- back home). In case of estranged women it's even hader.
Without ID they can't exchange larger amounts. It's also hard to create a new bank account on short notice without this.
My mother once helped a young woman set up a bank account. She had come to Mumbai to find work, and used to live at her aunt's place, and her aunt would hold her money for her (but skim off it). Most such people keep their savings in cash someplace "safe", though some use post office accounts. Anyway, the process was arduous. Her name was garbled on her family's ration card, and they needed the original, which was back at the village. This took forever to sort out.
This is going to be hard to work through for a few. Especially those with lower income who keep most of their life savings in cash.