I think it's a combination of a few things.

There are a lot of people who still have the mentality that ADHD is over diagnosed and is bullshit. That's a carry over from my childhood for sure. I see so many millennials still quote boomers complaining about ADHD these days.

Secondly, the current short form social media is decaying everyone's attention spans. As a result of this many people who may not have ADHD have some symptoms from damaging their attention span.

ADHD is likely more common than we give it credit for due to a lot of negative connotations to diagnosis, even today.

With all of that said. I am not a doctor, nor an expert. So take this with a grain of salt.

Edit: additionally, my doctor and much of what I have read said. A diagnosis is less important than understanding your strengths and weaknesses, how it impacts you and how you can build systems to remain effective in the areas you want to. So it matters less if you have ADHD or not, and matters more how you respond to the individual behaviors that lead you to believe you have it, and how you mitigate them. They did said, a diagnosis is most important if you are looking to medicate. That's the important conversation with your doctor.

I got my diagnosis under a year ago, and the way I've intellectualised it to myself is:

I'm in the top 5-10% for scatterbrained-ness or enthusiasm, or bottom 5-10% for working memory or personal project completion.

That's it. If I was among the 5-10% shortest people, I wouldn't have a "height deficit disorder", but learning some tricks would be helpful, there are tools (or in our case meds) to help, and I'd possibly need accommodations sometimes. Ideally the world would work on universal design principles and include the extremes, but unfortunately it isn't so. Same principle applies.