FF programs are the best profit centers going for the airlines. Imagine if the government allowed you to build a mint and print your own currency, sell your currency for actual profits (dollars), and then decide on your own whether or not to honor your own currency. I'll take that gig!!

The key is marketing: convince the pool of buyers that your currency will be honored slightly more often or for slightly more value than the "mint" down the street. That's what keeps your currency attractive to individuals and its value propped up among institutional traders (for example, the major banks that buy and sell billions of miles per year).

The upside to all of this (for us) is that most of the airline profit in the mileage game is thanks to people who buy miles all the time (whether by flying or through partners) but don't really pay attention to how the game works. They let their currency expire or simply never really use it well. That means there's room for people (like us) who have an interest in these things to maximize our return on investment in this artificial "currency market".

To sum it up: both the airlines and the savvy traveler are subsidized by the tens of millions of people who traffic in FF miles but never use them wisely or at all.