Why does Herot remain empty for twelve years in Beowulf?

Herot is the grand mead hall built for the Danes by
Hrothgar, the king. Unfortunately, this king is not able to protect his men from the
terrible monster, Grendel, who has plagued his kingdomfor twelve years. Whenever he is
hungry, Grendel slinks in at night, snatches up a handful of Danes (sometimes as many as
30), and eats them. Eventually, Hrothgar's men fear that if they sleep in Herot at
night, they too will become a meal, and they decide to go elsewhere. Hrothgar is not the
best of lords, since he appears ineffectual when it comes to protecting his men and
lords. He puts sentries along to the coast, but one never reads that he did anything
other than wring his hands, cry, and offer Grendel land and gold. Hrothgar's reputation
as a leader is trashed and his tales of woe travel across the seas. Beowulf, who is a
young Geat warrior and who wants fame and fortune, comes to the rescue of the Danes.
Herot soon is saved from Grendel's terrible menace.