Here is why Blackfish didn't feature at the Oscars. I've bolded the part in which Blackfish doesn't meet the required standards of a documentary. This is the criteria that the ceremony requires;
"An eligible documentary film is defined as a theatrically released nonfiction motion picture dealing creatively with cultural, artistic, historical, social, scientific, economic or other subjects. It may be photographed in actual occurrence, or may employ partial reenactment, stock footage, stills, animation, stop-motion or other techniques, as long as the emphasis is on fact and not on fiction."
I personally think it's one of the best documentaries I've ever seen, if not a little outdated. If she'd have left out the fiction then a blackfish would have won the award hands down.