I think the OP's point is that Japanese fans go ... all-in ... on the most minor details. They will arrive at DisneySea at 7am, wait in line for two hours, enter the park at 9am and then immediately go and sit down in the "front row" for the evening harbour show. And stay there all day!
They will line up for hours to "meet" a character, only to take a photo of the character. They don't even want to be in the photo! They could grab anyone else's photo of that character off the internet, but they want to be the ones to take the photo.
They will spend a lot of time (and money) inspecting every single item of merchandise in the stores.
Obviously the rides and shows are also popular, but the general theming, atmosphere, characters, shops, merchandise, restaurants and food, etc are also hugely appealing and all those elements will be on the ship/s as well, possibly even more immersively than they are in the parks.