The bundles are marketing, and as others have noted, since many of us use the same account to claim the codes, what's happening is obvious, especially as it's quite public here and has been discussed on Baen's Bar.
One message from Baen here would pretty much shrivel it up, but they have chosen not to do so. I would assume it's because those redeeming the bundles are also, eventually, making purchases. I redeemed several bundles and then began making purchases myself. We may redeem the bundles of books that are on offer at the moment, but we're then more favorably inclined to purchase those we truly desire. As a marketing tool to build good will with customers, it's worked extraordinarily well with me.