Certainly a lot of the last minute deal seekers travel on tight budgets. Some brag about being able to get off a cruise with basically nothing more than the auto tips/gratuities on their accounts and even a smaller percentage even remove those charges. I guess the cruise lines see it as a gamble. An unfilled cabin isn't going to generate a nickel of revenue whereas there's at least some chance that even a bargain shopper passenger will buy a beer or two.