User blog comment:TheRealD/Why won't Doflamingo uses his parasite ability on everyone in Dressrosa?/@comment-1595565-20150108061422

Has it not crossed anyone's mind that he simply can't? Devil fruit powers have limits. Bartolomeo can only make barriers up to a certain amount of surface area. I wouldn't be surprised if Doflamingo had a limit on the amount of string he can use at one time.