My hypothesis about this for a long time has been stimulants help everyone be more productive (with some tradeoffs) and ADHD is kind of a weakly differentiated diagnosis that could apply to most people. Probably something like this was lost when people stopped smoking, obviously beneficial for health - but a huge amount of the public was taking stimulants regularly via nicotine until relatively recently.
Your hypothesis is contracted by mountains of high quality scientific evidence. ADHD is a well-defined condition and there is an accepted way of diagnosing someone with it that effectively divides those with the condition from those without it. Stimulant medications may help many people to feel and be more productive, but that does not imply that people who meet the criteria for ADHD do not represent an identifiable…
Take a look at studying looking at the consensus on diagnosis. Even among psychatrists the same patient gets diagnosed with different things.