Why does Hrothgar promise Beowulf treasure?

Hrothgar promises Beowulf treasure as a way of showing appreciation and gratitude for Beowulf's heroic deeds in defeating the monster Grendel. This is a common practice in the medieval heroic code where warriors are rewarded for their bravery and accomplishments. The promise of treasure also serves to strengthen the bond between Beowulf and Hrothgar's people.