The business model is different. I think lines like Celebrity, as a Buick of Cruise Lines, have it particularly hard because they place their branding around the idea of the dining being enhanced as a reason to sail them and not their Chevrolet-equivalent division,
RCCL. The promotional strategy also undoubtedly causes customers to not make reservations because they might be able to get it for 50% off...
Disney also makes meals a key part of the experience, but by limiting the premium dinner options to one or two venues it means they are more likely to be full or reach higher capacity.