There is an obvious reason. He is afraid that Russia and the Russian people will follow the case.
Putin has been relatively successful in blocking the civil society of Russia from becoming strong enough and vocal enough, but I think it's quite obvious it's going to be more difficult over the years. One day the refrigerator will win over the TV set. One day people will realize that there are ways to live better in their country. That will be the case with Russia, too, one day.