That’s because nobody is looking for them because they all appear to be legal voters. When they do an investigation into voter fraud, they typically look at things like identity theft and stealing ballots. If you are mistakenly legally registered to vote because of these auto voter laws and motor voter laws, nobody investigate those.
If they enacted a national, verified voter ID, and actual verified proof to be registered to vote and to actually vote, and then stop automatic voter registration policies, we might see more of the issue exposed.