Why do people ume that everyone affected by Asperger's shares same traits?

The common stereotype is that we have no social skills whatsoever. There are several variations within the official diagnosis. I don't have all the symptoms of Asperger's. I know how to lie with a straight face. It makes me feel uncomfortable on a visceral level, but I am quite capable. I do know how to read people somewhat. Maybe my interpersonal skills aren't as sharp as that of the average neurotypical, but that doesn't mean they're nonexistent. I served three-and-a-half years in the military living a double life pretending to be someone else. So I've literally been forced into a situation where I had my back against the wall and I had to adapt. Another stereotype is that we all have a fascination with trains. I know absolutely nothing about trains. I have a mild fixation on maglev trains, but that's because I'm obsessed with green energy. I know very little about astrophysics, too. I love astronomy, but math is not my forte. I'm not Rain Man, okay? My specialty is geography. I am quite the expert on geography; that's why I'm applying to graduate school for geography. I knew because I have a natural aptitude for geography, it would behoove me to choose that as my major. Because I know so much about other cultures, I chose anthropology as my minor. People ume that we're all math and science geniuses. I'm not. My best subjects were history and english. I'm left-handed, so I'm more of a creative individual rather than a systematic person. We're not all the same, and we're not aliens or animals, either. So why do so many people ume we have all the same traits?