Maybe because most of the countries have already a currency that they are being used intensively, changing that parameter would be difficult when you have so much time used to dealing with your currency, plus, bitcoin is still really volatile, it can rise in price but it can also drop abruptaly, and that generates losses to the business that could implement it as a medium of payment
Naturally, all countries have a currency (fiat currency). And yes, most people are accustomed to paying with fiat currency.
People will change only when there are advantages in using an alternative payment method such as crypto payments.
So, a question is, "what about crypto payments is better than paying with traditional payments such as cash or card payments?"
From the buyer's perspective, crypto payments provide a way to make electronic payments without requiring a bank account or a credit card. For people that do not have access to banking services, or do not want to use banking services this is an important advantage. There are other advantages.
From the seller's perspective, crypto payments eliminate cash payments. Most merchants find cash undesirable because of the cost of processing cash and the security risk. Crypto payments are much less expensive than card payments.