Why are people with ASD so anxious?

If autism is not a mental illness, why do we hear about anxiety so much in relation to this identification?? Are we really that anxious?
Um...ya!
Anxiety is so common in autism because people are angry, upset, disappointed, or impatient with us all the time.

And also: those of you who are impatient: you know we are autistic, right? That we have a social communication disorder, and actually need to be taught the things typical, ordinary people just pick up naturally? Well if you do know, you sure don’t act like it.
Your practice seems to be shaming us for not knowing, rather than identifying the gaps in our understanding and then teaching to those missing skills.
No one seems to know how to teach us in the way we learn best, but they sure are quick to shame us each and every time we don’t measure up. I am so afraid to try because…well…I often misunderstand what is expected of me, or I just don’t know where to start.
I’m smart, but I cannot learn if I don’t believe in myself. I am now afraid to try anything, because I fear the wash of embarrassment I experience when I mess up. Again. Anxious? Of course I am.
There’s a solution.
Each and every child with ASD should be provided with a psycho-educational assessment so that teachers and parents can know how we learn, and how we manage in all of the areas of our executive functioning (jargon for some skills so important to school success—attention and focus, impulse control, organization, starting your work, time management, prioritizing, flexible thinking, and emotional regulation).
For too many autistic students, the speed and volume of the curriculum is too much and too fast, and this kind of assessment can help to figure that out as well. Once we have documentation of how we learn best, our parents can use that to advocate for the most relevant support.
They can make sure we are accommodated i.e. given the supports and teaching practices we need in order to learn the curriculum, rather than modified i.e. they take out parts of the curriculum to make it easier, or provide work that is grade levels behind our peers.
Obviously, it is cheaper and easier for schools to modify than it is to accommodate, but there is no way parents of children who are cognitively capable should allow schools do that to any one of us. We don’t want to be managed. We want to feel capable and respected-- and we want be educated.
. 
For many on the spectrum, the physical world also contributes to anxiety. Professionals know that up to 90% of people with autism have sensory and motor differences that are the cause of—or contribute to –our emotional or behaviour responses.
Simply put, environment can be overwhelming and often has us in a state of fight, flight or freeze. So loud! So crowded! So itchy! We never know where you’re going to make us go, or what we might experience when we get there.
Those noisy hand dryers in public washroom are painful, and the automatic flush toilets startled me so badly—I really needed to use the washroom after that!
Using our bodies can also contribute to anxiety—producing written work is so hard for so many of us, yet schools drag their feet in providing assistive technology while we fall further behind in our work.
We are often clumsy and not so good at team sports, which contribute to our poor social standing and aversion to gym class. The world around us is really quite frightening. Anxious? No kidding.
Here’s the deal: we don’t have to develop clinical anxiety, but we do. We do because of the lack of meaningful support, true understanding, and respect for our real, lived experience. 
Anxious? Of course we are.