When you go on a cruise, you need to factor in the tips for total price. Yes, it can seem like a lot, but the employees work really hard. I can understand that if a passenger felt an employee didn't do a good job or whatnot, you might not want to tip the full amount, but I think that's isolated.
I wonder about people who don't go to the dining room even once--if they are still tipping the waiters. I ate in the DR a few times, but ate mostly in the Windjammer Cafe. I noticed my waiters working in the WC. So even if you don't eat in the DR a lot, you still need to tip the waiters the full amount because they are working other places where they don't get tips.
I always saw someone doing cleaning. The employees do work really hard and IMO earn the tips.