Customer service response letter aside, isn't it likely Celebrity believes most people who book Sky Suites do so for reasons that are more important to the cruiser than just the dedicated butler? In other words, that those who book Sky Suites do so primarily for the overall Retreat perks and experience, and for the cabin itself, and don't really use the dedicated butler very much?
I can say from personal experience I used to book Crown Loft suites on Royal's Oasis class ships because I loved the Suite Lounge/Coastal Kitchen, the suite sundeck, the cabin itself, and all of the other suite perks...and never once even thought about having a butler. The concierge took care of most of my requests.
I assume this algorithm factored into their calculations before making the changes.