The point is that someone's honest mistake, or honest omission could be somebody else's lie and fraud. Perhaps what someone considered not a crime it is considered a crime by USCIS. Perhaps one had sex with a girl who said she was 18 and after naturalization she comes out of the shadows and says and proves that she was two days shy of her 18 birthday and there is a trial for statutory rape or something similar and then someone figures the guy is a naturalized citizen and someone goes and talk to ICE and they go ahead and try to denaturalize the poor fellow
Far fetched, yes, all a contrived story, yes, possible, I bet, fair, I don't think that would be fair, and that would be the kind of think a statute of limitations could help with.