Because the people who become software developers do that because at first it required a lot of focus and creativity. When they've done it for a while and have

Because the people who become software developers do that because at first it required a lot of focus and creativity. When they've done it for a while and have to implement the 34th variation of essentially the same thing, those are the same people whose mind wanders. When I did menial, boring work, my mind could wander enough to play blindfold chess with my colleagues without making illegal moves, and I'd still be productive. But when my mind wanders now, I already have a browser open and Reddit is a few touches away, and you can't browse Reddit at the same time as writing code. That's the other thing, there is a whole industry trying to grab our attention and keep it, and it's present in the same web browser that I use all the time during development.