The first thing to bear in mind is that this was a very competitive year among directors, a year in which one could argue that multiple directors were snubbed, including Bigelow, Quentin Tarantino (Django Unchained), Tom Hooper (Les Miserables), Ben Affleck (Argo), and even Paul Thomas Anderson (The Master).
FORBES: Why Did Kathryn Bigelow Not Get An Oscar Nomination For Best Director For Zero Dark Thirty?