Many people are arguing with the number, which I do believe is difficult to get a true number because many people go undiagnosed. However, many undiagnosed are also unemployed.

I struggled with many many jobs—from research scientist to walking dogs. I also have several degrees-summa cum laude/top of the class- and did not have a diagnosis attached to myself until recently (so no bias via employer). I also ace most interviews (I saw that as a problem in the comments). So the reason is very different depending on the person.

One thing is to get a good job, you really need connections. Though I am personable, it is very difficult for me to maintain connections and also use people in order for opportunity. Despite doing extremely well in undergrad and graduate school, I do not even get a chance for an interview for jobs in my field. All the jobs I have found and have seen others get were due to knowing people. So this is a difficulty in job searching for all people, but those with ASD have more trouble because they typically have less connections.

Secondly, jobs I have found —no matter how good I am at them, I burnout from being around people. And even jobs without people there are other factors (especially sensory ones). Most jobs do not have the flexibility to let employees take many personal days, that is just inherent in most jobs. I do not think having personal days would help my burnouts either, I would need months to recover from seeing people constantly and things like sensory problems often make some jobs impossible (for instance you may deal with something a few months but then it just gets to be too much and no break will be enough time to want to go back).

So from my perspective—someone who is intelligent with several degrees, can mask well initially, and no one would ever guess I have ASD because I internalize it—struggles greatly with jobs. So I can imagine the difficulties others have with it as well.