Because if there's other ways of managing it, why would you put chemicals into a person?
Knowing a person has ADHD gives you the opportunity to tailor things like their learning methods, tasks in a role etc to them.
My DH struggles most with focus. Either he gets hyper focused (usually at the wrong time) or he is very easily distracted. He knows if he needs to get something done by a certain time, he needs to clear any distractions and close his office door (usually has an open door policy). His team know if the door is closed, he needs to not be disturbed unless it's an emergency.
He's gotten where he is without meds. He doesn't need the meds. But he understands these things are to do with how his mind works and not that he's just useless (as his brothers spent many years telling him). And he knows how to handle it, mostly. Occasionally the hyper focus at the wrong time needs some intervention from me so we actually get somewhere or the things that need doing get done.
However, if he was just seen as a bit "flaky", people would just get irritated with him. Knowing why he's easy to distract (or hard to, depending), makes it easier to handle as someone around him. Doesn't mean I don't find it irritating, but knowing he's not just being a knob does help.