Like, sure Bilbo found the One Ring in a cave, but this was after the party had already found swords from the Hidden City of Gondolin in a cave. And yeah, sure, the swords weren't necessarily cursed or evil or anything, but they'd been lost a lot longer than the One Ring. Beleriand sank into the ocean during the War of Wrath! Meanwhile Sauron gets a paper cut and then Isildur drops the One Ring in a river and the One Ring vanishes for a few measly centuries. Look, the point is that sometimes you just find things in caves.