Final answer:
Demeter spends time with mortals at the home of Celeus because she is searching for her kidnapped daughter, Persephone.
Step-by-step explanation:
Demeter winds up spending time with mortals at the home of Celeus because she is searching for her daughter, Persephone, who was kidnapped by Hades.
In her search, Demeter wanders the earth until she arrives in Eleusis, where she comes across the home of Celeus. Celeus shows her kindness and invites her to stay at his home. As a result, Demeter spends time with mortals at the home of Celeus.