Chase could be looking at your income (or lack of it if your in college) and adding their potential credit onto what you already have when they come up with a decline, ie. if you maxed out all the cards could you make minimum payments? Speculation of course but I have found Chase to be one of the most liberal with granting credit.

As best and rrgg mentioned, ask why you got the decline, they must provide you with an answer, though you may be required to submit the request in writing. If it is too much current credit you can call and have Citi and Amex lower you credit limits.