Maybe because its that the average reader is a white middle age man? I know back in the 60's, 70's and probably before, girls comics were huge but for reasons I don't know (music magazines etc?) they seemed to die out. More diverse creators are emerging which is great so the future looks bright. I can only guess that if the vast majority of readers or fan base for the prog are white middle aged men its only natural that those fans who want to be creators are in the main white middle aged men? The more diverse the stories, the more the prog attracts other kinds of readers then maybe the creative teams in the future will be diverse too?