Because, like all major chain clothing stores, they have a supply chain going back to Cambodia and Vietnam and their full price is set at 10-15 times their cost. So on a 70% off sale, they still make money.
Major malls only want stores like this because this type of supply chain allows them to afford major mall rents - but this is why most malls have become so bland and generic and are rapidly losing customers.
But sometimes, even a large chain retailer can get overextended - as rents have become so high (to pay huge shopping center mortgages on properties that should have defaulted and gone back to the banks, but then would have to be marked to market value instead of fantasy - crashing the whole economy) that even the big stores can't operate profitably. Thus you now see the massive store closings by retailers who made the mistake of offering nothing special and thinking it wouldn't make any difference - that 2005 consumer spending patterns were here to stay.
Watching the gyrations being undertaken to maintain commercial real estate values at their current astronomical levels has been quite a cabaret show. The side-effects on the "real" economy have been just as devastating as the dreaded crash would have been - but the banks are still getting to play "let's pretend" indefinitely.
I do not remember the last time I went to a mall at all