My Father was like that. Brilliant scientist and founder/CEO of one of the top 25 biotech companies of 1990. Started and left unfinished more projects that I can count.
His excuse was that he would get back to them, but the newest project was taking all his attention...until the next newest project.
He said it was because he had more interests than time. I always said it was because he had no self discipline and that excuse is just bullshit for not being able to focus on priorities or make a proper plan.