Because fb knows the user is male and odds are this would attract a click.

click looks remarkably like dick when set in this context.

True. They probably know if you're gay also, so in that case they might do it.

This is generally because softcore pornography for women do not concern penises. Women seem to prefer exposed male chests.

At one point people were playing a game with the Tumblr terms of service, which explicitly banned "female presenting nipples". Subjective standards of offence always result in ridiculous cases.