Thanks for the replies everyone. It's definitely a different business model than we are used to, but obviously its working for them.
The majority of our cruising is on higher end lines (river cruises or Windstar in Europe), but when we stay within the US it's 90% Carnival because we mostly do short Mexico or Caribbean weekend cruises. In all instances we know what we are paying (all in) at the time of booking and if a cruise price drops, that's great- more shopping money! 🙂 The concept of not really knowing the "all-in" price prior to booking just seems kind of odd. If I go according to the $99/per day rate that means I'm going to potentially spend $4,500 on this cruise (5 night cruise on the Mariner, suite, drink package, dining extras). If I under estimate, we can still pay it but it may mean going over the allotted vacation budget which we dislike doing.
Certainly gives us something to think about! We may end up at an all inclusive instead.