Being tall gives you an obvious advantage at basketball. As a result many tall people are drawn to pursuing a career in basketball. Could it be that ADHD gives you an advantage at the kind of tasks involved in software engineering, and that many people with ADHD are naturally drawn to this kind of work, even though the advantage is not so obvious as a physical characteristic like height?
The traits often looked for in software engineers when hiring can often bear a striking similarity to the traits an ADHD or autistic person may display.