Because both Hinduism and Buddhism originated in the same region, they both spread quickly throughout Southeast Asia.
EXPLANATION:
There are various religion which are followed by people and among all the religions Hindu has the most number of followers and then follows along with Buddhist.
There religions are very much worshiped and the rituals that have been found and studied defines the true meaning of this life.
Both the religion spread in a rapid amount in a very small amount of time.
