The card lets them know you almost care.
The true brilliance in the offer is keeping the dollar value so low as to make it not at all worthwhile to churn. Sadly it’s no replacement for dollar coins, Amex travelers checks, savings bonds, or prepaid debit cards.
As Lucky says,
you might be limited to 99 cards and might have to enter your address each time, but if you don’t value your time and are looking for all of 99 miles, this is the deal for you.