Probably because there's no such thing. Gays do go on the Disney cruises, but there's no organized Disney Gay Cruise Week.
Simple, just ask the people making the booking if they wish to sign up for any of the gay events or take advantage of the gay discounts on park hotels.
Except Disney doesn't have any "gay" discounts. Should they offer some?
Yes, there is. The cruise takes place just before gay week.