Actually, that is precisely the case here. Your friend doesn't have enough miles for the reward because she has not flown enough. She is trying to pool miles from your account to get around that. As a frequent flyer, I do not want that to be free and easy. I want that to cost you guys an arm and a leg. Otherwise, there would NEVER be a seat for me when I go to redeem my miles.

You are thinking of frequent flyer miles like money. You have $5 and your friend has $5 and that should be a total of $10. Instead, think of frequent flyer miles like green stamps (I know I am dating myself here). If you have 10 green stamps, you can't redeem them for squat, and they are worthless. Same if your friend has 10 green stamps. If you have 20 green stamps, however, you can redeem them for a prize. This gives an incentive for the frequent, loyal green stamp collector. Any yes, all the people out there with just a few green stamps have a goal to reach for. This is the whole point of the program.