I am still of the opinion that RCL doesn't make as much money off of repeat cruisers as it does off of new cruisers.
Repeats are less likely to buy pics, take the expensive excursion, go to the spa AGAIN, and know their way around a coupon book like no others. They know that onboard sales are ripoffs, and how to get a pricedrop faster than most TAs. And OBC? They know more about this than RCL! These are experienced bargain hunters! And I believe they spend less and less on board every time they cruise.
I also believe RCL knows this through tracking so this move was a calculated gamble maybe to get Diamonds to aspire to Diamond Plus and fast.