Most people don't even understand what "understanding/accepting disabilities" means. They superficially say we should all be accepting and understanding of differences because they want to sound like good people, but they do the opposite. When it comes to an invisible disability like autism, it's even worse. It's the same as having a "zero tolerance for bullying" policy and yet allowing/encouraging bullying to be very prevalent in a workplace (like where I work). Basically people don't even understand those things because they don't care at the bottom of their hearts.
If they do care, like the case of your mother, they do try to understand and learn. Unfortunately, most people don't care, and are not interested in understanding or learning. It's a sad reality.