They just want you to buy their overpriced wine onboard.
But think of it this way, most States don't allow you to bring a bottle of wine into a restaurant to have with dinner (except of course it's in Oklahoma - unless they changed the laws since we were there).
Personally, I don't mind paying a bit more to buy a bottle of wine onboard a ship, but I really object to paying 3 times what I can buy it for off the ship. Beer and mixed drinks are marked up, but not much more than an average neighborhood bar, which is fine. And I understand the concept of making a profit, but the price gouging they do on wine is criminal. When you figure they probably buy the wine by the hundreds of cases so they get them at a really reduced rate, the overpricing they charge is ridiculous. This is one of the reasons I really like Holland America - you can bring all the wine or champagne onboard that you want to - I've seen people bring on cases of wine. No corkage fee if you drink it in your stateroom. Plus, we'll bring a couple of glasses with us for dinner and never had any problems.
While I feel Disney is overpriced for what they charge for their cruises, one good thing; you can bring all the wine, beer, and alcohol onboard that you want to.