[nijuashi]

Being unable to focus attention is not a beneficial trait in current society. Imagine having to have to take regular medication to control your blood pressure but cannot keep track of your regimen. It requires extra effort to keep the person healthy. Another is tackling difficult and long-term cognitive tasks, which is often necessary to function in society nowadays (I dread filing taxes). This may change in the future (especially with AI) but right now it is the way it is.

There are many traits that are advantageous in one environment and not in another: for example, sickle-cell phenotype became prevalent in regions where malaria was common, because you are likely to survive the infection. But otherwise the individual is likely to suffer from sickle cell anemia. People who have low calorie requirement may survive a famine, but may suffer from obesity in calorie-rich environment.

Many things are hard enough for “normal” person who would not be perceived as having ADHD, but it’s more so for people with it. The expectations are set by the modern society, but the actual challenges for ADHD are naturally present - thus they are classified as disorder. It’s commonly debilitating enough to be recognized as one.