why bitcoin is still illegal in many countries of world

Is there any solid reason behind this ??/
The prohibition of bitcoins by some states is a problem of those states. Bitcoin is a legal system. States illegally define everything they can not control.
But the bitcoin can not be removed from the ban.
Bitcoin can't be banned. That is the problem. It is not a physical asset, and therefore the government can't prevent its entry or exit from their jurisdiction. Also, unless the coins are converted to fiat, the authorities can't track them.
Yeah. That's why the states do not like bitcoin. Because they can not get tax from the money earned with bitcoin. Only when they are converted into cash and transferred to the bank account.
But in the future we can use bitcoin without converting it to money. Then they will not be able to follow in any way.
This is just one of the reasons. Another reason is that the government does not control the number of bitcoins in circulation and cannot use the issue to manage the economy of the state. Additionally, bitcoin is a direct competitor to the dollar, and who let it? But there is good news. Until they do not consider bitcoin a currency, the taxes he no need to pay.
But in the future I think that the states will go to a system like bitcoin. They will create a system in which Bitcoin will become centralized and controlled.
Especially the blockchain technology is being examined by the finance sector. States can do something like this because of its fast and secure nature.