Originally Posted by
MrkGrismer
My guess would be because you can have different characters in different guilds, so with BtA you could buy discount potions with your character in a high level guild and then give them to your characters in a low level guild (or unguilded characters). Thus allowing a character that is not in a guild to get guild discounts, or guild discounts they would not otherwise qualify for.
IMO a better solution would be to add some sort of 'guild tagging' to items such that a 'guild tagged' item could only be used (and/or sold) by members within the tagged guild, that would also eliminate guild chest thieving. But it would probably take considerable effort to implement.