The reason why crypto is banned by some countries is because their government is afraid that the crypto market is a bubble that could make their country's economy suffer and make their country lose control
They think that it can be misused and cause the threat to many citizens of their country which they do not want to make it happen . Also they think it could create more scams across their financial and this will make it more threat as then already country may be investigating other scams and this will add more work to them.