In my setting dragons are basically covetous demons, the more something is cherished or desired by mankind the more they want it. They feed on feelings of avarice, envy, grief from loss.

Thus their lairs are filled with gold but they go in more for refined bars/minted coins rather than raw ore (they'll still take it). Cut gems, jewellery, fine clothes, exotic perfumes, famous works of art, all ideal plunder, especially from people who'll spend the rest of their lives missing it. If a piece like a painting is eventually forgotten about and fades from history, the dragon will destroy it to make room.

They of course also abduct people, magically imprisoning and enslaving them. Musicians, playwrights, religious leaders, monarchs. Public fame and adoration is good but love that is especially powerful and true is their favorite union to break. Same rule as above, the dragon will keep them sustained and even beautiful, but if the person is forgotten about or say their lover accepts and moves on from their grief, they're dead.

Burglary and rescue operations are expected and desired. A dragon with a low value hoard is weak and vulnerable, ripe for stronger dragons to cannibalize or a dragon slayer to target. There are even famous thieves who "soften up" a dragon by thinning its horde before a slayer takes a shot.