Leo was fantastic in The Aviator.
Recent biopics nominated for best picture and the actors who were nominated with them:
2013: The Wolf of Wall Street - Leo DiCaprio, Jonah Hill (probably a little loosely defined as a biopic)
2012: Lincoln - Daniel Day Lewis (won), Tommy Lee Jones, Sally Field
2010: The King's Speech - Colin Firth (won), Geoffrey Rush; The Fighter - Christian Bale (won), Melissa Leo (won), Amy Adams
2008: Milk - Sean Penn (won), Josh Brolin; Frost/Nixon - Frank Langella
2006: The Queen - Helen Mirren (won)
2005: Good Night and Good Luck - David Strathairn
2004: Ray - Jamie Foxx (won); The Aviator - Leo DiCaprio, Alan Alda, Cate Blanchette
2001: A Beautiful Mind - Russell Crowe, Jennifer Connolly (won)
2000: Erin Brockovich - Julia Roberts (won), Albert Finney
I may have missed some, but I'm a bit pressed for time. But I think what we see here is that in the last 15 years, the Academy has never nominated a biopic for Best Picture and snubbed the entire cast of acting nominations. In fact, biopics that get nominated for best picture are far more likely to have multiple acting nods.
So, anyway, it's just odd.