The 3 and 4 day market out of Florida has always been fiercely competitive, relying much more on the local market for passengers rather than fly cruisers.
20 years ago, the best food was on the smaller independent lines. Dolphin IV was little bigger than Tugboat Annie but the cuisine was fabulous. Premier Lines had some of the old Homeric Lines classic vessels and an executive chef called Norbert Finger who was as good as they come.
The last time I took a short 4 day cruise was 2 years ago on NCL and the food was just as mediocre/good as their Jewel class ships were then offering.
In my experience, it does not matter if you're paying $40 per diem or $200, the MDR is going to serve the same food from one cruise to the next. If they're going to eliminate "free" lobster, it has to be a fleet wide decision/policy as cruise lines live or die according to passengers' expectations which are largely based upon a consistent product.
So why are cruises sold at ridiculously low prices or even given away to low "rated" casino players?
It is not just a matter of high vs. low season demand. Sometimes, as with repositioning cruises, there are just too many ships being moved from one geographic area (Alaska or Europe) to another at roughly the same time, which usually co-incides with low season. Cruise lines know that if they can capture the repo sector, many passengers will also pay a higher per diem to take the preceding and/or following cruise to create a 30 day "grand voyage", a sort of poor man's world cruise segment.
Then whenever you have countless ships operating in a market like Miami/Port Everglades, there will almost always be a "loser", the ship that loses out in the beauty stakes; besides, can the cruise industry as a whole correctly estimate the carrying capacity of the market each year? There are probably in excess of 100,000 cabins that need to be filled in that same market. If absolute demand is for 95,000, then some ship will start the discounting.
Unlike the airline industry where flights can be consolidated and airplanes re-assigned, there is a lot of inertia in the cruise industry with a ship rarely withdrawn once positioned for a season.