Until now, Bitcoin is hardly accepted by countries for what it is because it is [1] beyond their comprehension, [2] a threat to their existing fiat system, [3] is neither issued nor directly monitored or supervised by the government, [4] is not owned by a certain person or company which the government could easily communicate, convince, or even threaten when the necessity arises, [5] is somehow anonymous, [6] and so forth. Having mentioned all these reasons, it is really difficult for Bitcoin to be accepted as legal tender in any country.
And you've said it all. No government would want to run a nation without "being in charge" especially when it comes to the country's finances. I guess some countries are trying to devise ways that they can adopt this technology and still be in charge of the circulation of crypto. But till then a country like New Zealand chose to apply the normal tax policies to any crypto payment instead of saying no to cryptocurrency.