I can't imagine why

I completely agree with you....

I notice there are only five players who are credited. And it's a fairly big cast too. As you say Ward Bond's character was so involved in the story there really is no sense in not crediting him. Anne Revere ought to have made it to the screen credits as well playing Jessie Florian as she did. Even though Turhan Beye and George Cleveland only had walk on parts they are distinctive actors who also didn't make it to the credits.