Why are Democrats so determined to keep non-citizens on the voter rolls?

Why are Democrats so determined to keep non-citizens on the voter rolls?: For years, we have been told there is no voter fraud and illegals don't vote. No matter how many states violated their own election laws in 2020, we were told that the election was pure as the driven snow. 

But, the U.S Justice Department is suing Virginia to not remove ineligible voters from their voter rolls, of which there are a lot. And, of course, we are told by the media that the Justice Department is absolutely impartial. If they were impartial and only concerned about having legal citizens vote, wouldn't they also encourage getting people who aren't citizens off the voter rolls?