More specifically, they said this practice serves as a very strong discouragement from indie games ever participating in bundles again, because the bundle economics depend on many (most?) of the keys either not being redeemed, or being redeemed by people who would otherwise not purchase the actual game. But when people who want the game are able, many months later, to pay a fraction of the price for a key sourced from a bundle, this really hurts sales for the game and makes the bundle a net negative instead of the positive it's supposed to be.