Answer:
Hinduism, which was the major religion in India around the time that Buddhism began to pop up and still is today, revolves around a cast system. In this system, you were assigned a societal role at birth, and that role could never be changed. Most people who weren't nobles or priests didn't like this system because it encouraged oppression towards lower class groups. Buddhism provided a way out of that system, which made it quite popular among lower class Hindus who wanted a way out of their situations.
