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.
It is not about that the government is scared of bitcoin, it is more of that it is something that they have no control over it. Satoshi envisioned a place where people would experience financial freedom- where every transaction is made public and unalterable. That is the reason on why the blockchain technology exist for this purpose.
Now that cryptocurrencies is one of the ways in achieving financial freedom, the government somehow wants to control the transactions under its wing. They see it more of a threat than an actual danger in any case since cryptocurrencies had been used for illegal purposes in the future.