Because the policy of a country will certainly limit some of your activities in the transaction.
in this case the central bank was included to monitor your financial activities.
“Russia’s Finance Ministry supports the idea to limit the amount cryptocurrency that can be purchased by individuals,”
Source : http://www.altcointoday.com/putin-confirms-russia-will-regulate-cryptocurrencies
we can only pray and hope that each state government can quickly establish the rules about the bitcoin so that all of us who are active in bitcoin world can be comfortable and calm in their activity.