Believe me when I say that even the government in most of the countries that has failed to make Bitcoin a legal tender wants to invest in Bitcoin because even them have seen Bitcoin's potential but unfortunately they won't be able to be in control of running it like the way they control fiat currency. They know that they will lose control over monetary policy and regulations so they rather not legalize it so they will keep being in control, and the other reason why they have not legalized it could also be because of lack of proper understanding of the potentials of Bitcoin.  But the major reason why they don't want to legalize Bitcoin is because they know that they won't be able to control Bitcoin.