Not trying to be a cruise line policy advocate, but please don't make this a big issue. Usually new policies are a reaction to occurences or events. Beverages in suitcases get heavy and may not be packed well and the multitude of bags being handled, sometimes roughly, is enormous. Containers get broken and passengers get mad because the porters did not handle their luggage carefully. With the new policy, case closed..the beverages should not have been there. this scenario is probably one of many that led to this printed policy.
Another factor could be over-abuse of the previous policy, and I honestly cannot imagine a hometown restaurant saying it is ok to bring your own beverages at all. A few cans and no one cares, but when truckloads arrive and they have to hire additional people to carry them on, it is a problem.
Please try and not let a 6-pack of your favorite beverage get in the way of a great vacation. Slip one in and don't say anything and I bet you'll be fine. Bring the pantry along and get tagged.