I think that a lot of anxiety is possibly "learned anxiety" in the sense that people on the spectrum realise after a while that they can never really know how neurotypical people in the next new work, educational or social setting are going to react, and when the next "attack" experience is coming (so often in the form of namecalling like "you're weird"). Being treated unkindly is one thing, but the unpredictability and social humiliation are added stresses which accumulate over time.
Some anxiety is no doubt due to neurotransmitter differences which have been found on the spectrum, but not all I think - we are social creatures, yet so many of us end up with social anxiety after having been publicly shamed for often trivial social errors. This situational competent of learned anxiety is ignored by therapists, it seems, so that the victim of social shaming is just not supported nor really acknowledged, but viewed as an intrinsically anxious person with an internally generated "anxiety disorder".
In one sense I see anxiety disorders as communicating a history of unhealed, unacknowledged, attacks and wounds; people on the spectrum seem generally so quick to internalise all blame for any perceived defect. In another I see this prevalence of anxiety as representing the strain of living life on a continual tightrope when walking in every kind of social situation - an ever present anxiety about the next fall, always trying to make it to the other side unharmed.