I've never heard a good rationale. I understand women-only events, because then women can take their abayas off -- but FAMILY events means married men are present, so it's not like the women can let their hair down, so to speak.

Judging from enforcement, "family day" has always meant "no laborers" -- they've just usually framed it in sexist rather than racist terms, which are marginally more socially acceptable here.