Why didn't Buddhism become Popular in India in Lord Buddha's time? In Ancient India when Prince Siddhartha became Lord Buddha, Buddhism started. After that so many people in India followed Buddhism. 



As per this Map in India shows very little stats having Buddhism, so my question is if Buddhism is a very good religion why didn't it go all over India, Why is Buddhism not popular in India in Lord Buddha's time?
Okay, let me start by saying I'm not a super religious person but having lived in Srilanka, right next to India and a Buddhist country qualifies me to answer this.

Indians at the time of Gautama Buddha were mostly Hindus and had a caste system where the Brahmans, the teachers of Hinduisms were on the top and the poor was at the very bottom. The poor literally had to jump in to the drains when people of higher castes were traveling on the same road. The Buddha, however, opposed the caste system and he was very ambiguous about the creator deity Brahmans and Eternal self Atman and rejected them both.

So, there were somewhat of a tension between hindu brahmins and buddhist monks. The Buddha however did not deny the existence of gods (devas) and said that the did exist in other worlds that is better than our world but are subjected to the same samsaric sufferings as humans. They too die but they have much larger life spans compared to us. Humans can go to these heavens if they do enough good deeds and when it runs out, they will be reborn depending on their karmas. 

Buddhism attained prominence as it was supported by Royal courts and virtually disappeared from India after the fall of the Guptas. By the 8th century Shiva and Vishnu.

However, Emperor Ashoka who ruled most of India from Afghan mountains to Bangladesh was greatly responsible among other kings for spreading Buddhism around the world. He created Nalanda a huge library containing Buddhist documents and even some Hellenic people turned to Buddhism during his reign as well as Pakistan and Afghanistan. He sent his own son and daughter to Srilanka with a branch from the tree that the Buddha attained Nibbana and ordained the king and the royal court at the time. 

Troops from the Muslim Malmuk Dynasty later destroyed Nalanda, along with a huge number of Buddhist scriptures and eventually the Boh tree the Buddha attained enlightenment was cut down. The one in Srilanka is still there and is the oldest tree in the island. Events like these and Hinduism coming back to the royal courts gradually decreased the number of Buddhist followers in India.