Some of the biggest super powers are afraid that if they make Bitcoin legal the total economic power will shift from the hands of the authority to the control of Public. This is rather good for the common people in a specific country as the currency will totally be decentralized in its own way and will be community driven but it affects the overall corruption and can totally block it in anyway which would further affect the pockets of the individuals manipulating the current system and they would never let it happen.
Most of the people in the authority tend to avoid the argument by saying "Bitcoin Transactions can promote uncontrolled scams and illegal deals" but it just avoids the facts that same thing is still happening even if we use fiat, still much of the illegal deals are ongoing in the current economy and usage of fiat does not stop it in any way. As the currency is growing its usage and power every day a large sort of community is getting attracted to Bitcoin, which make the government and banking industries in powerful countries worry about it and they try to boycott the use in whatever way they can to keep the power in control.
By looking at the currently increasing interest and adaptability of Bitcoin and other crypto it will surely perished in the powerful countries in the future due to the advantage of Bitcoin which favor to common people than the currently powered authority.
I would be very happy to list an example of Venezuela's latest government authorities cryptocurrency
Petro which has just helped a country to overcome bad economic conditions is a effective way.
Expression of the Powerful Countries towards fiat.