But why they ban bitcoin and some country still not make bitcoin legal in that country ?
Well, it is just a matter of choice. One country can see cryptocurrency as an opportunity to utilize for their own economic or financial interest while another county may view it as a big threat to their economy and the financial control they are traditionally utilizing. In other words, we all have differences and since the state has the sovereign power we could not do anything if a country would choose to ban the selling/buying of Bitcoin within their jurisdiction. Technically, though, they could not touch Bitcoin.