User blog comment:Fliu/Chapter 926: Hungry Hungry Hippo/@comment-7614831-20181201083707/@comment-2600:1702:3C50:A6E0:4512:89CF:ED02:FD7-20181202001950

It could also be because the fruit is an imitation rather then an exact copy. Devil fruits were probably never created in-universe with the intention of their creator (if they have one) that they would be duplicated.