The other problem with a custodial sentence for false claims is that it might result in the false accuser not retracting the claim for fear of a sentence, so it could have a more damaging effect dragging out the situation until the accused has enough proof that they are innocent. It’s easier for a false claim to be retracted when there’s no recourse for making that claim. It’s a shit thing to do I’ll grant you, but the current set up is probably best right now, until every human gets tagged/implanted or something (which is another terrible idea).