Unfortunately, the world is still full of a lot of people with ignorant and bigoted views. While the cultural conversation around sexuality, gender and racism has been ushered to the forefront, ableism remains one of the most pervasive and least discussed societal ills out there.
The mainstream understanding around mental health and disability - both physical and mental, is still very limited. Public campaigns and even television shows in recent years have helped create better understanding of autism as a spectrum disorder, and how being atypical is a very different experience for every person. It's statistically likely you've met people with ASD without even knowing it, because they didn't match your preconceived cultural notions of what having autism means.
In a recent Reddit post, an ableist customer freaked out and demanded a refund when she realized the person making her mug is on the spectrum.