Beowulf and the dragon's treasure

On page 111, lines 1612- 1619, it says, "The Geat captain saw treasure in abundance but carried no spoils from those quarters except for the head and the inlaid hilt embossed with jewels; its blade had melted and the scrollwork on it burnt, so scalding was the blood of the poisonous fiend who had perished there. Then away he swam, the one who had survived the fall of his enemies, flailing to the surface."

Beowulf saw the bountiful treasure of Grendel and his mother, but he didn't touch it. Then why was he so eager to send Wiglaf to fetch some of the treasure of the dragon? What was the difference between these two hordes? Why was it not okay to steal from Grendel's mother's horde (even though he had killed both of them) and okay to take the treasure from the dead dragon?

~Hannah, the confused reader of lost treasures and dying kings