That may well be, but it doesn't mean that NCL's agreements with their suppliers need to reflect that. Flavored Vodka is crap, but marketed like it is something special. That's a different marketing scenario than going toe-to-toe with other suppliers of good Vodka for the vast majority of ship revenue. If NCL includes their product in the drink package, they will sell tons. If they price it even $1 higher, they likely won't. It's all business, and it doesn't have to make sense to the average consumer.
NCL: "hey Bailey's supplier, I'll include your product in our standard package if you sell it to me 10% cheaper"
Booze distributor: "nah, pound sand"
NCL: "we'll do that and talk to you again when you aren't happy with how much less we're buying from you"
Wash, rinse, repeat.