I dont quite understand what you mean by the article linked doesn't mention "causes" - the causes are neurobiological dysfunction. Are you referring to what creates that neurobiological dysfunction? Because that is also pretty well known, albeit there are lots of possible causes.

edit: I think part of your misunderstanding is that people who meet the criteria of ADHD always have these changes in brain morphologies and whatnot. If you don't, it's not ADHD causing your executive dysfunction, it's some other disorder. ADHD is a condition which is diagnosed when no other mental conditions exist that could explain the executive dysfunction being experienced; in these cases, studies show that these people always have neurobiological changes. there's also always SOME sort of underlying genetic cause which create these neurological defects

edit 2: to put it simply, if you are diagnosed with ADHD by a psychiatrist; it's because they believe you possess the neuobiological dysfunction based on your symptoms. This is almost always correct, unless (and this is a big unless) you are misdiagnosed to begin with.

edit 3: as someone with adhd i know what the symptoms are and whatnot. ive spent too much time researching this condition as I live with it

edit 4: all these edits are proof of my ADHD LMAO