It seems to me that lots of people consider the ability to focus as some kind of innate ability which we are all born with, it's not. It's a learned skill which requires practice. Stop practising and it atrophies.
We all understand this for physical exercise, I think we need to understand the same principles apply to skills.
Working at a gig where I couldn't have my phone really put me on a painful dopamine fast, but helped me remember that I actually can focus. So I started working at the library and leaving my phone at home.
Well, some people are innately physically stronger than others.
For some things its just the truth that some people have "the drive" and some people don't.
I don't buy this. I think people find it easier to make excuses about lacking some magical, unobtainable, abstract property like "the drive" than to actually put in the effort to improve themselves.
People over diagnose themselves so it seems more common than it is, but adhd is definitely real. Its not merely attention, its a set of traits like reduced working memory (and ability to utilize it) that manifest as difficulty in sustained attention / distraction. People who have it do a lot of other funny things than simply "get distracted easily", just ask the spouse of any person with add what _their_ coping strategies are and you'll get many humorous and perhaps unexpected stories.