Modern game used prices are insane to me too but sometimes it's the only way to get something "unique" for a modern player. As discussed, there is an abundance of material out there for any one player, but when you factor in game used, sometimes you can find yourself a totally unique item for an oversaturated market and player.
For example, here's my Mike Trout career hit #410. There is only ever going to be one of these, which makes it a cool Trout item and is much more interesting to me than a bat he used for batting practice that is technically "game used":
