I've always considered it a legitimate request when people want to live with others of the same gender for a shared room in their home.

For example, you especially see this on sites like Craigslist when people are seeking roommates. This policy seems to overturn the ability of hosts to do this. If I were a female in an all female home renting out one room, it would make me uncomfortable. Perhaps other do not see this as an issue in short-term renting, but I do.