Making Bitcoin a legal tender means when a person goes to purchase a commodity, instead of paying with dollar or whatever currency is being used, they pay with BTC.
Given the unstable nature of cryptocurrencies, and the untraceable nature, would you suggest it wise for countries to adopt Bitcoin as a legal tender?
Recently, El Salvador and Central African Republic announced that they have adopted Bitcoin as a legal tender.
Given the nature of the market and Bitcoin's features, they are preferred to have a technology that they can control and urge people to pay taxes which is likely impossible with Bitcoin.
Some countries decline to have Bitcoin also because they believe that this is one reason that helps to increase criminal activities. They somehow put some blame on it because of its anonymity feature and instant sending (possible).
Though people are preferred to have this kind of system, however, the adoption is going slow due to a lack of support which sometimes discourages especially for merchants and other establishments owners.