Stuttering is an invisible disability. We look completely normal and able to function, therefore we must be. Sometimes we can communicate effectively, therefore it's "not that big of a deal". Stuttering is also associated with the stereotype of shy/nervous/socially awkward people, who'll always be shit on by society. Stuttering probably won't ever be fully recognized by the general public for what it is: a neurological condition. But every other disability and condition that you mentioned are either clearly visible upon first impression or are unquestionably recognized as disabilities. That's why.