state wants to get tax. the input and output of the money can not be controlled. also a serious competitor for bankers. also a good way to make money. countries are opposed to it. a money they can not control is troubling governments.
Well there could be more reason than this. As we all know that the system could also be use in a good way like its features like the blockchain technology where transparency really matter. As it could be use in a government department to let the transaction be incorporate to blockchain. However, some countries do not allow the use of crypto like those countries who are always at war because it could be use in a wrong way.