During the covid revenge travel period (Once things started going back to normal) it seemed every cruise line (including
DCL) was booming which caused all of them to knee jerk IMO and start rushing to order more and more ships. Many of these ships holding 4000 + guests (across the cruise industry not just DCL). So lots of beds to fill while more and more port cities are not as friendly to the cruise industry.
The cruise lines have also started to both out price their guests and cut back on offerings in the last year- from Carnival switching up their loyalty program, to NCL charging for extra entrees, to both Royal and DCL raising prices on their newest ships to eye watering levels. I personally suspect that the cruise industry is in for a rude awakening in the next few years in the US if there is any economic downturn (which always happens eventually). It will be interesting to see if DCL keeps their commitment to 13 ships. It would not be the first time Disney announced a project and walked it back (looking at you Tony's Town Square Theater and Mary Poppin's ride).