My thought, and to be clear it is only my thought, is that DCL doesn't so much care about loyal clients anymore. There is little profit in bringing back the same clients time after time. A client who has sailed DCL once will buy the t-shirt, the captain Mickey, the hoodie, the tervis cup. Probably pick up a new t-shirt and a stuffed bear on their second cruise. They buy less and less on each cruise they take because A) they already have the items that are a 'must' B) they don't like the items that they haven't already purchased so no point in making that purchase. I for one only take a cursory look in the shops now and have not bothered to buy anything in our last four cruises. I have what I like and there is never all that much new.
My theory comes from talking with a friend who was a CM. He told me that the Wonder and then the Dream was the cash cow for DCL as they did two cruises every week which meant they sold two of everything that the 7 day cruises only sold one of. There was more to this but that is the basics.
I think DCL just doesn't care as much about repeaters, they still sell to us but they are looking for the new cruisers so why put a lot into perks? They make a few changes every few years and take away what they can. This may change once their fleet has grown by two ships but for now I don't believe they are to concerned. Their ships sail full and they are getting the price they are asking. If they push a few repeaters out, well, the first timers will come in and spend their money in the shops. Again, JMO.