Why do people think Autistic people aren't sexual

I have autism and I really don't understand this stereotype that we aren't sexual or think about sex. Sure maybe we don't always go around talking about wanting to suck dick or or fuck somebody but that doesn't mean I'm not sexual at all. I actually love BUTTS! I'm a huge butt girl lol. It's just weird that some people think autistic people are like asexual or don't understand sex. I understand sex. I'm sexual. I get horny. I masturbate. I watch porn. I do all!