I imagine that was for the benefit of GMs (in-game customer support). Occasionally they'd be responsible for spawning loot for guilds who had just spent some ho

I imagine that was for the benefit of GMs (in-game customer support). Occasionally they'd be responsible for spawning loot for guilds who had just spent some hours fighting to and killing a boss, only to have the server crash afterwards and wipe out their rewards. By making the loot table a property of the instance, and attaching the last instance a player was part of to their character, the GM can just do a lookup to see what items were missing after the server reboot and hand them out. The only thing they have to take the players' word for is that the kill happened, rather than whether or not some ultra-rare reward was part of the missing loot.