When most of a country doesn't have access to digital payments, lack of cash is a problem. Although to be fair, the poor aren't the ones trying to buy things with large denomination notes anyway.

More than 50% of the population of India doesn't have a bank account. A large percentage of Indians use an open field as a bathroom and have trouble getting access to clean water. How does this help them in _any_ way?

Hold on, let me spend time walking 10 miles to a bank and sign up for electronic payments instead of tending my field and barely making enough to survive on. Yeah, while this is great for India's banking industry to get some growth, I hardly see the benefit for the significant rural population that does not have easy access to a bank nor any of the supporting infrastructure that is required to support electronic payments.