People are loyal to a brand because they are comfortable with it. As long as the brand keeps them happy and they feel that they’re getting valued for what they pay for they stay.
Once you’ve cruised many cruise lines and realize that the products are very similar in many ways and it’s the little perks that get people to go back. Weather it be casino comps, free alcohol, free laundry, a meal at an upscale restaurant, or just the ability to get on and off the ship early - everybody has something that they feel is a perk that gives them extra value to the cruise fair that they pay.
Actual cruise fares have gone up across-the-board but I believe more on Royal than anybody else. However, if one books early on a group fair or gets a casino comp there are some affordable trips to be taken even on the more expensive fair ships. I I am sure though that Carnival if they could figure out a way of increasing the base fair, they would do it in a heartbeat. Even if it meant giving out more free drinks or a luggage tag to every single person.