In previous financial disclosures American Express has indicated that miles are the most expensive type of redemption, and they work to encourage other uses. It is to our advantage when the popular press reports that frequent flyer miles are difficult to redeem, or offer poor value, because it encourages some people to redeem for giftcards or merchandise. Keeping the average cost per point below budget is beneficial.

I assume, but do not know for certain, that American Express obtains some type of price concession from their partners when they offer transfer bonuses. In other words, the incremental cost of the promotion is probably shared between American Express and the partner.