I think there are a lot of factors.

1. Wealthy Americans often already have access to or utilize services that would help someone with ADHD manage their symptoms regardless of whether they get a diagnosis or not.

2. There are so few affluent Americans left that it’s a significantly small percentage of the population already, meaning though they are more likely to have a diagnosis available to them, they make up a small percentage of people who actually have ADHD.

3. Poor people have less overall knowledge about learning disabilities and Neurodivergences on the whole. They assume that because they also have the same symptoms (which they don’t recognize as symptoms), it’s a matter of laziness, a moral failing, or a lack of work ethic/ability to buckle down).

Also If you’re poor, it’s likely that you may not be evaluated at all (which is part of the reason so many adults are now being evaluated and the percentage of adults who have ADHD has gone up rather steeply).

Also also if you’re poor (especially if you’re a minority) you may not get a diagnosis because there’s a stigma attached to it (nobody want to admit there’s “something wrong” with their kid developmentally).

4. When I was a kid, there was also a lot of assumptions about who could have ADHD (girls “didn’t” get ADHD, it was a boys disease). And ADD was considered a separate thing. If my mother hadn’t worked in the education system it’s likely I and my siblings never would have been tested at all.

5. Support systems in schools are lacking, underfunded, understaffed, and unsupported. Lots of kids fall through the cracks, even when they aren’t neurodivergent.

6. Even less people have access to mental healthcare and for those that do it’s still exorbitantly expensive even with insurance.

7. Without healthcare it’s unlikely that you can get access to medication. ADHD meds are considered narcotics /schedule 2 drugs. Can’t get them without a prescription.

8. Some doctors have a propensity to treat people looking for a diagnosis as addicts looking for a fix. It’s not just doctors (looking at you pharmacists).

Edit:

9. The symptoms a lot of us share are at odds with the way the medical system works, meaning we’re likely to have trouble getting the will to talk to the doctor, have trouble keeping up with appointments and doing tasks that might be required. I was diagnosed as a kid and I still haven’t talked to my doctor about getting further help when I already have a diagnosis.

To be clear, doctors who specialize in this often have a more streamlined process with our symptoms taken into account but just getting to that point where their system can take effect is daunting. The medical care system in this country as a whole works against us.