Board Thread:Manga Discussion/@comment-86.141.78.224-20140923111712/@comment-26928757-20150830024523

Because Araki didn't think about it. After releasing a few chapters w/ the sons, he was just like, "crap!" and quickly wrote a note saying that Giorno probably was there, but for some reason did not appear in the story (don't remember which chapter it said that in, but I definitely read it) xD

...And yes, I am joking :P