There is a difference between gift cards and AmEx MR points.
With a gift card, say a $100 gift card is activated, you actually do need to do provision of $100, to fund the payment of $100, and this $100 is not a profit. There is also a hard expiry of the gift card, say 3 years by law in NSW, so after 3 years, if the gift card is not spent, the $100 gift card can be disabled, you know that the card holder can no longer get her / his $100 for sure, so the $100 provision can be safely removed, and the $100 can now be moved into profit. (this is how some of the FMCG companies I worked in function with this type of number moving)
The problem with AmEx, is there is no expiry date with MR, meaning if they do it as per above, then their provision would just sit there forever with no end in sight. Tell any financial person that there is no date on a movement (provision in this case) and they would make sure that their displeasure is known.
This is not about profit, this is about keeping the book tidy, an accounting practice.