The reason why cryptocurrencies are not successful as a medium of payment varies from region to region, and country to country, depending on how exposed or developed the people are. Ideally, the majot reason has to be that it is not as easy and convenient to use as compared to using cash.
I would give an example of the question, How can older people and children use crypto currency in everyday life? After all, the fact is that cash not only because of people's habits is the most desired way of paying bills, but also the ease of use plays a very big role.