Why would anyone volunteer to direct a film?

I've seen a million "the making of" films but I've never seen one as candid as the one that comes with Jane Campion's Portrait of a Lady [DVD]. Mrs Touchett is a key character in the book. In the film she's not as prominent. That must be because she was played by Shelley Winters, who was seventy-six at the time and, as "the making of" makes clear, a nightmare to work with. She can't or won't remember lines, snaps at everyone around her, messes up take after take and has to be quietly bollocked by Campion in front of everyone. "Shelley, listen to your director." The other actors, hanging around for hours in agonisingly uncomfortable Victorian costumes in the heat of an Italian summer, just walk away. You can see that they want to scream. You come away from it wondering why anyone would ever want to direct a film.