Maybe I'll revisit it later in the year when, like Carnival, Royal Caribbean promises online booking. But the details were sketchy, so I couldn't avail myself of its online booking feature. Windjammer requires users to submit a form. Early-bird deals are by far the most desirable. Best of all, if prices go down subsequently, early birds will get a price adjustment.
Late birds get discounts too.
Consider the largest ship lines first. The ships that cruise these waters are huge. They need to fill space early and capture last-minute voyagers. Many such cruises are promoted by offering two-fers, kids free or reductions for frequent cruisers. Many ships have to reposition from one route to another as the seasons change.