I think it'd because of (4), the reactivity of gold atoms, or rather, it's unreactivity. Gold, unlike most metals, doesn't form an oxide layer when exposed to air (Which is why it's so valued in jewellery, the metal will never tarnish, only stay gold forever). This makes it weaker, and so it can be formed in to thinner sheets.
However, (3), the nature of bonds between gold atoms also allows for the metal to be flattened, as metallic bonds aren't amazingly strong, and allow for metals to bend. This is what makes pure metals so weak, and why we use alloys.
