In part, I think it's one of the ways he mimics the form of books like Beowulf or Gilgamesh or other works of that sort—that kind of thing tends to be full of digressions and whole scenes that simply seem like mistakes—dragging down the "momentum", not "advancing the plot"—if you're going by modern very-focused standards of what constitutes acceptable plotting, which of course is the kind of thing most people are used to reading/watching.