If I recall correctly, Savage originally only dropped 1 weapon on Floor 4.

When they added Weapon Coffers to Savage in SB(?) (I think? Or was it Armor/Accessory coffers first, and then weapon coffers in ShB?), they didn't replace that drop, they just added the Coffer "for free" to the "second chest" that previously contained mostly fluff/junk like mount keys and minions.

So basically, the extra weapon is just a "bonus item". If no one wants it, none of the loot budget was actually lost.

It's one of the few non-deterministic "spin the roulette" aspects of the loot system remaining, and since it's not "stealing" any intended loot from you, it's best to just think of it as a lootbox/gacha draw or something. If you get a dud, eh.