I think because of their country?.Because we all know that russia is a very very big country.And bigger country is equal to bigger population.Most people there are internet people means their life rotate on internet.And also some terrorist live there and maybe they use bitcoins for illegal things online.Thats my opinion
I'm from Russia.
And I, and most people are very poor (the thieves and crooks in the government are destroying the country's economy), and Bitcoin for us this is part additional earnings.
Another reason is paranoid the government's desire to control everything and everyone. In Russia there is a religious and political inquisition, that is a negative comment towards lawlessness authorities, or repost, or like in social networks, can condemn and imprison or condemn arbitrary, and because of this block the bank account or bank card thereby depriving the people's livelihood. And this is one of the reasons for the use of uncontrolled ,by nasty government, Bitcoins.