I would guess it has less to do with your flying and more to do with your credit profile and desirability as a credit card customer. They're probably doing statistical modeling based on what they know about you, your credit history, outstanding credit, etc... to determine whether or not you'll be profitable and low risk customer to them. One thing to keep in mind: paying your balance in full every month is NOT profitable for them... and in the end your potential value to them will drive how much they're willing to spend (ie, how many miles to buy for you) in order to keep you...