Because if they didn't, I would stroll into my local jeweler (I live in the Palm Beach area, if that helps) and buy a few Patek Philippe Nautilus watches (at 35K each) on my SPG card (call it 150K bucks). I would then walk out of the store and get something to eat.

Leaving the mall, I would return to the watch store and return all of them, asking that the return credit be applied to my bank ATM card.

Volia, 150K miles in 1 hour. Feel free to stroll on down to the Louis/Gucci (or any other high dollar label) and repeat indefinitely. You could probably get a million miles in one day (if you had the credit limit to support it) and get it all refunded to your bank card.

This would also serve as a "no cost" cash advance. Buy a thousand dollars of crap on your CC. Return it, credit the return to your bank card. Stroll down to the bank and withdraw 1000 bucks.. Volia, free cash advance (with points earned, thank you very much) against the card you originally used.

If anyone ever finds a store that will actually allow you to do this (refund to a different card), keep it to yourself! I think that the FT community would put the store out of business pretty quickly with the buy/refund technique; it's like the coin gig, only easier and faster (you can flip your entire credit limit in one day, and probably with just one transaction at a jewelery store).