I think they started putting dehydrated pumpkin in it just to shut people up. But pumpkin is actually not an ingredient in most pumpkin spice things.
Looked it up, the two things I missed was ginger and cloves. With the cinnamon it has a little heat to it. Honestly I neverminded pumpkin spice it was just kind of popular to hate on it because a certain demographic couldn't shut up about it.