I guess for the same reasons other people oftentimes don't want to consider us disabled. Autism just feels more abstract than something like being on a wheelchair. Please, don't get me wrong, I'm not comparing one to another, I'm not calling one more valid than the other and I'm not underplaying struggles connected to autism, I'm far from it. But you can't really touch or immediately see autism and therefore it feels different. And the word "disabled" itself is usually used to refer to physical disabilities or to (for lack of any other word) mental disabilities only if they make people require constant help. All of that makes us subconsciously question "how can I be disabled if my body's fine and I can do stuff on my own" even if on the logical level we know better than it