Is the poor parenting you mentioned just putting the kids on the drugs or is there usually something before that makes the kids get ADHD?
Before that.
There are loony modern parents that ascribe to the theory that your kids are leaders and you should allow them to do as much as possible without correction, and when you tell them what to do it's optional if the kid actually does it. This results in kids that constantly try to push boundaries because kids need to know where the boundaries are. The kids, especially boys, then get into a pattern of always looking for boundaries which, over many years, results in ADHD.
This one kid I'm thinking of, if his parents let him he can play Nintendo all day. They don't usually allow for that (one of the few boundaries they have is electronic screen time) but when he has special days he can do that non stop and he has no problem with attention span at all. I saw this firsthand before they put the little fucker on medicine.
So he doesn't have a chemical imbalance or anything, it's that you're raising an asshole who has no respect for you as parents. But go ahead and give the (((pharmaceutical companies))) money instead of figuring out why your kid sucks.