I have a brother who works for Disney corporate. He says that the Late Booking discounts go to the cast members so they can take a cruise at a discount rate. He did make a note that he is only allowed to book 2 weeks in advance for the cruise. The problem is not so much the short cruise time required, but their 2-year-old child.
Much like Disney had an allotment of how many people they can have on a boat, they also have an allotment of how many children are allowed on the boat. This never affects the consumer because we pay retail price for the cruise. This allotment tells the staff if they need to hire more people to work in the child care service or not. For paying customers, Disney has no problem adding more staff. But for cast members who get a large discount (I think it's almost half the price), it does not pay to have them cruise if there are too many children on the boat already.
Just thought I would let you know
Matt