During the events of a game, the key to a chest in a house could be "off the map", maybe travelling with its owner, maybe lost at seas or during a drunk night out and lying in the muck under a grille, but unless there's a good explanation, owners should really have theoretical in-game access to their chests. People hiding their valuables during times of crisis is not unheard of, though. Maybe the owners got killed and the location of the chest was lost along with the key. Maybe they didn't get rid of all their illegal items and got docked anyway. Then you have thieves/pirates hiding loot, dead letterboxes, and so on, but I absolutely agree that while we may never know the story to every hidden cache, item drops should be part of the lore in RPGs. BG3 did a good job with most I've found. After all, there's a war going on, Harpers and Zhentarim moving about, goblins, cursed shadows,...sufficient reasons for chests, keys and their owners to get lost, or found by unexpected player characters.
