The USSR is no more. If these Russian transplants would like to become citizens of Latvia, they are welcome to, but they don't want that for some reason.
One more time, for possible penetration into your brain: they are not transplants. They are the grandchildren of those who were forcibly relocated there. It's not even the sins of the fathers being visited onto the sons. It's a matter of the sin's of people who hated the fathers being visited on the sons.
Meanwhile, of course, the Latvian government sponsors parades for Latvian veterans of the SS. Those are your kind of "good citizens," I guess.