“Why didn't I get in?” is an understandable question, and while we can't address your specific case, we hope these notes help you.
In general, know that we get a very strong pool of applicants and that we only take a class of twelve, which typically translates into our making offers to less than 10% of those who apply. In other words, the admissions process is very competitive.
More specifically, with regard to the files, here are some areas where we find shortcomings:
Statements of purpose that are poorly written and/or don't indicate much reflection and/or don't transcend “I want to learn how to use (equipment),” or “I knew from an early age that I wanted to be Steven Spielberg.”
Test scores and GPAs. The graduate school has low-end thresholds of 3.0 for GPAs, and 82 for TOEFL scores (international students only). While we do sometimes petition the graduate school to make exceptions to these low-end thresholds, scores below these thresholds do not help your case.
Know that negative letters of recommendation are extremely rare, but letters of recommendation that are bland, generic, and/or short indicate that the recommender either doesn't know you very well or does know you and doesn't wish to communicate his/her true feelings. Additionally, we ask for three letters of recommendation. If fewer than three are submitted, we interpret that negatively.
Of greatest importance is your creative work. While we rarely get samples that are “bad,” your work needs to stand out. Can you tell a story? Is it a story worth telling? How derivative is the work? Is the work juvenile or mature (which shouldn't be translated as “We don't like comedies” - in fact, we do.) What sort of command do you have over your craft?
Also with regard to your creative samples, know that it's very difficult for us to judge collaborative work - e.g., where you co-directed with someone else. If something works, who should get the credit? If something doesn't work, who should get the blame? Additionally, with regard to creative samples that you did not direct, while some crafts such as cinematography and editing are relatively easy for us to judge, others such as producing are not. Know that while we do sometimes admit students solely on the basis of, for example, their cinematography work, we primarily look for evidence of storytelling ability and/or an overarching creative vision. We also do occasionally admit students who don't have film or video in their creative portfolio, but those students are at a disadvantage when compared to the majority, who do.
Lastly, know that our admissions committee of four rotates on an annual basis. If your file did not get the response you were hoping for this year from evaluators, know that a different group of people would be evaluating it next year. However, you should keep working - i.e., don't presume that your work which didn't get you in this year will get you in next year. Keep writing, keep shooting, keep cutting, keep working.