One of the symptoms of #ADHD is hyper-vigilance, sometimes described as "scanning behavior". That is to say, an evopsych[1] model of the motivational difficulty of ADHD is that in the ancestral environment, while having some people in your village who are able to keep focused on a task is good, you also want to have some people around who are constantly looking around to see what's goin' on everywhere, easily prompted by the environment
[1]: for the record, yes I know this means "pretend"