I think it's pretty safe to assume that these companies have non-trivial amounts of IT infrastructure (that needs maintenance, migrations, upgrades, etc...). Any such system that doesn't require knowledge transfer must satisfy at least one of the below:
1) You have an oracle stashed somewhere.
2) You have volumes of documentation.
3) Retaining key people that actually do know the system.
4) You don't ever plan on upgrading/migrating and are content with the current system for perpetuity (I'll even throw in that it's trivial to re-image a computer when its predecessor breaks down).
We know 1 doesn't exist, or at least, no offshore company has one that they can assign to Carnival.
2 requires a team of engineers that pore over those volumes of documentation, make sense of it all, not fuck up any future plans with their 0 experience of the Carnival systems, all the while sticking around long enough such that said team can maintain the system, return a profit for the IT company for real services rendered, and learn enough to plan out/implement whatever upgrades/roadmap they decide to do.
Good luck with 3. I rarely see management being able to retain the right talent, even when it's not pressured by offshoring schedule and with relevant leads still in place. That and human nature to retain your friends.
So that leaves us with what? 2. Which means Carnival will never improve, and for sure I won't want to go on their cruise now. Or maybe you can come up with 5/6/7 etc..., which I'm all ears.