BroBear--they never give feedback as to the exact reason you failed. It may have been a COMBINATION of the sim and the interview/questions.
It might be worth finding some coaching on interviews. At the very least, try and remember the questions they asked, write them down, research some more typical questions and then PRACTICE. Not just sitting and reading the question and 'thinking' about the answer but rather have someone play the role of interviewer and VERBALIZE you answer. Knowing what you are going to say and actually saying it (especially under the stress of in interview) are two different things.
They expect you to know the 'type' of questions that will be asked and to have appropriate answers. For example: a very common question is to ask the candidate to 'give an example of a time when a captain did something that you did not agree with. How did you handle it'. The answer could be simple or complex - but you need to answer it!! You might get away with not being able to answer one, possibly two, such questions but that is it. I know guys who have LIED just to give a reasonable sounding answer.
Get some interview practice and do some research. You'll make it!!