Because it cannot be tracked and most of the countries do not allow the use of crypto because it can be used for illegal activities with no record and the government cannot do anything if something bad happens.
I imagine if crypto is applied as a legitimate means of payment, every transaction that is abused and fraudulent will be a big problem, and of course it cannot be traced clearly, the state has a fear of legitimate accountability, in this case it is still a common fear because there is no the right rules to regulate it.