Can you pass around a crypto currency physically? I don't think so.

The main reason is that you are thinking in the context of a "modern" country, try to travel around villages in Africa and you'll see why cash is still king. Somewhat recently a lot have started using extensively mobile cash, using literally any phone which can make calls (which I think is genius in terms of accessibility).

Of course, you could base their mobile cash off crypto but that doesn't make any difference to the user.

But that requires a strong and stable mobile network infrastructure which one cannot take for granted over here.