Ok, hear me out on this one.
Dragons hoarding gold to sleep on it.
We assumed dragons are greedy bastards like us Humans.
BUT
When you're a creature with a mass of thousands of tons you need a bit more than memory foam to sleep comfortably don't you think?
Gold is a soft, ductile material, a good heat conductor (keeps you cool) and stays untarnished (perfect for century-long naps).
Nothing to do with greed, dragons just want a good mattress!