When people can’t talk it can be because they can’t manage the complicated fine motor skills that are involved in manipulating your larynx, and if they have problems with fine motor skills they’ll probably have problems with using handwriting or sign language too.
People with autism and other neurodiversity may also have other impairments that prevent them from speaking, such difficulty initiating movement, disorders of timing between their thoughts and speech or echolalia where people repeat words or phrases they have heard and are sometimes unable to say what they really want to say. Some neuro-divergent people cannot speak under ordinary circumstances but can speak when their bodies are simultaneously doing something else like playing the piano or riding a horse. For these clients it often helps to slow down their pointing speed as they often want to rush everything and slowing down can help a great deal with accuracy.