Do they actually believe they will ever own that money just because they keep yelling : "mine, mine, mine!"?
Maybe with fiat, sure. But not with Bitcoin. Not your keys, not your coins.
This isn't about keys, this is about claiming ownership if those coins are ever deposited into an exchange in the (far) future. I've seen enough questionable judge rulings to not be surprised if some judge in some country would go with this.
It's beyond stupid: if the coins are actually abandoned, they can't access them. But if someone moves them 20 years from now, that proves they weren't abandoned. There is no "claiming abandoned coins" in Bitcoin.