NAB rejected me as well, first card i have ever been rejected for. Made no sense to me as I had previously had the ANZ Black Frequent Flyer card, I have The Amex Explorer, The Westpac Black Altitude, The Citibank Signature. I have all my cards paid off every month. I have a exellent credit rating according to the credit report i got done.. It was the strangest thing but i heard NAB are very finicky.
As well as i kept getting asked more and more things to fill out and more calls with questions etc, it was such a long drawn out process only to get rejected at the end. I was not happy with it.