1.Why Samudra Manthana happened?
Vishnu Purana describes that sage Durvasa in his state of frenzy
threw the garland at Indra, who caught it and placed it on his
elephant Iravata. The elephant was irritated by the fragrance
of the nectar in the flowers.So it threw the garland to the ground
with its trunk. Irritated sage Durvasa cursed Indra and the gods
to lose their powers which is what necessitated the famous
churning of the ocean of milk to obtain Amrita.
2.According to Vishnu Purana, goddess Lakshmi is the daughter
of Bhrigu and Khyati. She resided in Swarga with other Goddesses.
Sage Durvasa cursed her and forced her to leave Swarga and
settle in Kshirasagar. She rose up during the churning of the ocean
of milk–Samudra Manthan between the Devas and Asuras.