For the lawmakers it has an added bonus of being a double bind for transmascs. Passing for cis isn’t binary or consistent, every trans guy has to guess what the likelihood is that any time he uses the men’s room someone will think he looks trans and call the cops. There is no safe answer for him (trans women have a similar situation). For both trans men and trans women the less likely to get the cops called answer will tend towards men’s rooms, but that’s only because men are less likely to call the cops on a woman in the men’s room.