That can not make them money long term. If that were the case they would build ships with fewer cabins. Sailing with empty cabins is no way to build a railroad.
Sure, they ask and put it in your profile. Then when you get to your cabin, you can ask the attendant to separate them. The default is together as cabins are made up quickly the morning of departure day.
Allowed gaming the system is still gaming the system. If you book a guarantee, keep it. Don't make someone who books later and pays full price take that connecting cabin