Why do women directors get no love from the Academy?

Indiewire had an article today about major contenders in the Oscar race. In its entire history only 4 women have been nominated and one has won and that was 2010 ceremony to Katherine Bigelow. The article stated that Bigelow will most likely get another nomination for the film Zero Dark Thirty. People with different nationalities have won all the other categories, I think it is interesting that only one woman has won and no other has been nominated since her either.