The main reason maybe they won't their citizens are not reporting their wealth to hiding from tax and this could affect a country economy crashing. They are still not find the way how they could manage their people if they are legalize cryptocurrency so right now it's the best way to ban it.
Also not all people in a country are smart enough to own cryptocurrency which the price sometimes fluctuative so fast, maybe for some people will drive them crazy to see it's price if they hold crypto and these won't be govement's responsibilty

There is country as for now does not support the use of the cryptocurrency and the bitcoin itself we know that its decentralized and the bitcoin does not have any taxes and many investors and large amount holders using this coin to prevent the taxes, some of the country banned due to different reasons might possible such as the illegal action using bitcoin. If they cannot regulate this coin some of they banned that transaction. But still not all people know already the use of cryptocurrency investments.

In some countries people are using bitcoin as their earning and they tend to save money for their own good which is good but some of the this countries they dont have a law for taxing cryptocurrency. So in their perspective, its like you are committing tax evasion although it is legal.

To be precise, Bitcoin cannot be completely banned at all. Because Bitcoin does not belong to a certain company or organization, it can be said to be closed. Bitcoin belongs to the tens of thousands of people who own Bitcoin. As long as there is a network, Bitcoin can survive.
To prevent money laundering and prevent illegal transfer of assets.
Bitcoin is a currency that cannot be regulated, so it must be killed in the cradle. However, Bitcoin has been banned again and again in many countries, and it has come back again and again, becoming more powerful.
Many countries have already recognized the reality and know that the wheel of history is constantly moving forward. Instead of being abandoned by the times, it is better to learn to keep up with the pace of the times.

Simple answer is ..

" If they cannot control then they will Deny" that is simple reason why Governments are banning and not allowing the use.

because those countries that already accepting bitcoin and there are already adopt bitcoin as legal tender knows the betterment of their economy can be helped by Bitcoin .

Let them ban bitcoin but let others welcome it thats all.

The government is a system designed to govern subjects who happen to live on the territory the government has control over. To effectively govern those living on the territory, the ruling class has an exclusive right to exercise violence. This is essentially a monopoly on the use of force, which the non-ruling class obviously shouldn't have.  As we all know, monopolies aren't a good thing because the lack of competition leads to worse products and services. Moreover, no one can protect you from the government itself: you're not allowed to use force. No one can, except bitcoin. Bitcoin is not a violent force nor an aggressive means. It is purely defensive technology that makes you self-sovereign, monetary independent, and free. Governments don't like such a state of affairs, they don't like the idea of you having a defensive tool to lower their influence. They want you to be dependent on them, otherwise, they won't have full control over you. They are trying to ban bitcoin so that you can't use it to escape.

BTC was being used as a bridge for other people like drug dealers and terrorists to make illegal transactions in which the government won't be able to stop them. With that being said, online transactions made through blockchain technology is out of the government's hand so they cant properly monitor and intervene with such illegal activities

At the moment but different countries have accepted bitcoin legalization. Again some countries did not legalize bitcoin. However, in countries where bitcoin has not been legalized, there are many problems.You have given very little in the least developed countries. And has given legitimacy to bitcoin, especially in developed countries. And in all the countries where legitimacy has not been given, there is a problem

Different Countries have different views over Bitcoin. Very few take it on the positive side whereas the majority have a negative opinion over bitcoin. Now this has been gradually changing with the massive number of active participants on the cryptocurrency market. Even governments have begun to legalize its usage on all needs.

Most of the government that are against bitcoin usage at present believe on a statement, bitcoin will affect the country's economy. Maybe in the future these countries will realise on missing the right moment.