if it were for CMP, there would be nowhere near enough rooms for all the people..
on average, a team has at least 10 students and 2 teachers/mentors/parents come to CMP, and the vast majority of teams have 30+ people. Now multiply by the 235 teams that are already committed to CMP this year (plus the 100+ more that will be added as the season goes on). That's over ten thousand people already. Which is about five times the number of people on a cruise ship filled to capacity.
Now, with a regional, it's much more plausible, though personally I'd say it would make more sense to have in on a
docked cruise ship. That way the public can still get in to see the competition, and if spare parts are needed, you're not taking a helicopter to the nearest island.
I think most large cruise ships also have a large dining area where the tables
might be able to be moved, but other than that, finding a space for pits would still be challenging, unless they were split up somehow.