Themes, characters. Because O'Neill was a "great man" he did not have to follow the rules of ordinary mortals. I see this sentiment expressed (hesitantly) by the author, as well as by his wife Carlotta.

I saw the same thing with my father. Always being excused from his fatherly, husbdandly, other duties, because he was a "great architect". Perhaps this is why it is so difficult for me to accept O'Neill's failings with his children. Too close to home.