I can't believe that 1,200 Russian women all would rather not know. More likely they thought doing what the owners of the service wanted would enhance their chances of success.
By the way, knowing about criminal background would hardly insure men with records couldn't get a bride. I know there have been FR threads about European women who start by being pen pals with an American man on death row and then want to marry him.
It's not just European women who do this, there are plenty of American women too. It's a liberal pathology.