Causes for the decline of Buddhism in India

The revival of Brahmanism and the rise of Bhagavatism led to the fall of popularity of Buddhism
The use of Pali, the language of the masses as the language of Buddhism was given up from the 1st century CE. The Buddhists began to adopt Sanskrit, the language of the elite
Deterioration of moral standards- After the birth of Mahayana Buddhism, the practice of idol worship and making offerings
Attack of the Huns in the 5th and 6th centuries and the Turkish invaders in the 12th century destroyed the monasteries
All these factors contributed to the decline of Buddhism in India