Because all frum women are either pregnant or nursing at any given time and therefore shouldn’t be drinking 🙂
In all seriousness though, it’s probably a tznius thing- people do stupid things when they drink too much, which for a woman would be considered un-tznius. Although really, no one, male or female, should ever be drinking to the point of acting stupid.
For the record, I do drink, but only wine, and not more than 2 glasses at a time. I even drink while pregnant or nursing, but only a little little bit- doctor says it’s fine.