He says so in this interview:
He chose to move to Russia and accept a permanent residency. He (and his lawyers) have expressed the desire to acquire Russian citizenship eventually as of 2020. The war with Ukraine has changed the political calculus everwhere. Snowden must be feeling caught between the devil and the deep sea.
As someone leaking secrets and overtly critical of American polity, it is hard for him to return to America. Certain jail time awaits. He hasn't been pardoned by the last two presidents despite numerous requests appearing in news. But now with Russian aggression, he finds himself locked in a country where quality of life, freedom & personal security is falling faster than a dropweight. He cannot choose another secure country. Worse, he could be blackmailed by Kremlin to be a state actor/mouthpiece in exchange for his personal security guarantees.
Tough choices.