Cash is better because you can easily use it to buy your needs anywhere in the country/world. You pay cash when you buy street foods, for your children's allowance, to pay for public transportations. People also are accustomed in using cash in majority of their transactions.
Yes you are right many countries dont use bitcoin as method of payment system. But still bitcoin is better than cash because you can still do a lot of things with bitcoin online. You can buy anything. Cash is used for the purpose of buying things. So that we use bitcoin for that purpose. Bitcoin is better than cash in all aspects.