My guesses are one or more of the following: that you maybe didn't fully articulate how you could add value to the class, your reference letters might have been inconsistent with the rest of your application, the essays are poorly executed, your career goals are either unclear, unrealistic or too many other people want the same thing. Or, they might have gotten just a lot of people with your profile and similarly high stats. Plenty of applicants applying to Columbia with an investment Banking background. I'll be willing to take a look at your application of you like.
Farrell Dyan Hehn, MBA
Admissions Consultant & Verbal Strategist MBAPrepCoach.com