Given we do not know what causes ADHD, and there is disagreement over whether it is a difference or a deficiency, its quite hard to have any definitive answers about it.
Given symptoms of ADHD include things like being better in emergencies and being able to to focus more intently on certain things my view is that it is a difference that society is unwilling to tolerate and is therefore treated as a problem to be fixed.
So you could argue that if you are on the boundary, whether you have ADHD traits to the extent of being a disorder depends on the environment you find yourself in, and so you could characterise that as some aspects of that environment 'giving you ADHD', but it's still not yourself changing.
Deficiency, since it gets in the way of successful, effortless living.
People say they "suffer" from ADHD and use it as an explanation why some things harder for them than for others, etc. Many complain. People classify it alongside other mental health issues.
It's a bug, not a feature. Would anyone without it wish for it? Would anyone with it and given the choice for it to be gone choose to keep it?
Balance. The inability to "focus" attention at the likely relevant thing as a matter of course is suboptimal. You don't want to get distracted by the wrong thing when it is a matter of life and death.
I don't know that your theory is any more likely than a theory of ADHD being less likely in those before-times because it would get you killed because you're not paying attention to the right stuff and nature then stomps on you. Not that I have any reason to believe this idea.
Being good in emergencies is not a trait you need often, but very valuable when you do need it.
I think of it like the doorway effect, the working memory is dumped more often to have more resources for processing sudden events.
ADHD is most often regarded as a problem in children. Children are generally expected to behave in ways that are hard for those with ADHD (sitting still for long periods etc.) to an extent that adults are not.
Lots of things make your life harder. Lots of places where being a woman, or having the wrong skin colour or being gay got in the way of "successful, effortless living" and we generally took the view that society needed to change. All of those have been treated as mental health issues to at least some extent (e.g. "hysteria" for women, hormone treatment for people like Turing) too.
Being too intelligent can be a problem too. Does that mean high intelligence is a bug?
> Would anyone without it wish for it? Would anyone with it and given the choice for it to be gone choose to keep it?
Why would anyone want to be good at dealing with emergencies, or being able to focus intently on things they are good at?
Today we don't need sci-fi/cyberpunk movies/books to actually have that as properly diagnosed biological/psychological problem, not many know how to deal with unless you get prescriptions for soft-amphetamine variance given as a medicine so one can kill extra thoughts running crazy inside or... go mental and/or depressed. and trust me.. I have 2 at home. so it's not that I'm judgemental.. it's just my daily routine to deal with a challenge that outside drug.. slowing down and getting offline.. actually helps equally vs. everybody believes we can be celebrities online for 72h then nobody cares... actually never cared so here comes the attention drama to 10k other thoughts, brains tells you is important.
I can assure you... all the online mess ain't helping all of you who suffer it, unless you're brilliantly intelligent people (many are) who are highly functional, considering the energy burnout that requires you to stay above the water line.