I know I often see people write things like "we feel guilty for going on a different line form our usual "fill-in-the-blank".
And I often wonder why they say that. Now of course I understand "loyalty programs", etc, but this is something else - these people have formed a real bond with these cruise lines, and I think in many cases I think that in their minds they believe the line has come to know them, and they feel guilty for going elsewhere like they are cheating.
It is probably because they meet certain people on board - like the cruise director, who they have a conversation with about the CD on a sister ship, and they have "mutual friends. They also know the waiters and some of the room stewards, (because it is not unusual to see workers you know move around from ship to ship).
Or it could be like our old friend Goldfinger (?) who just knew a certain cruise line was the best because, I don't know why, I guess he "did the math" and figured it out.