Autism refers to Autism Spectrum Disorder. There is nothing wrong with using "on the spectrum" for people with ASD. There are also several usages of "Autism" by itself, so I don't know where you got the idea that it is being treated as a bad word.

There's a bit of nomenclatural history here. There was autism, which usually manifested as a severe disorder that significantly impaired functioning. People with a social deficit like autism, but who were otherwise fine, were usually diagnosed with Asperger's syndrome, which was considered like autism but not quite autism. Then there was high-functioning autism, which wasn't the same as Asperger's syndrome, a major distinguishing characteristic being that people with HFA had a speech deficit in early childhood while people with AS did not.

That was where things stood as of the DSM IV. Then the DSM V came along and lumped all of the above into a single classification of "autism spectrum disorder".

Because people aren't saying the word autism outright and are using euphemisms, like bad words are.