Adding to this, it could do with a long-held regret it wants to resolve before dying. Like not having a keepsake from a long-lost love - a few of her scales if another dragon, or a lock of hair if she's humanoid. Something only the dragon would consider valuable for instance. Or maybe the love is a lingering ghost and the dragon wants the party to put it to rest so the dragon itself can drift off to "sleep" finally unburdened.
Those would both be extremely important to the dragon (who, for all its power, is immobile), but be fairly low-stakes as quests go.