This is a random bonus offered to players even without having o send money to their betting accounts. It could be either a reward for loyalty or a welcome carrot. Either way, the player gets to benefit because they can use it to play various games in the casino and get tangible wins.
Russia is the birthplace of vodka, and it still produces the best "little water" in the world. Restricting gambling is a policy priority in Russia, as the fall of the Soviet Union saw the emergence of a black market for games of chance. Currently, mobile online gambling is illegal and international sites are actively blocked.