India is predominantly a Hindu nation. For the Hindus cows is what Mother Marry is to the Christians. Cow is the symbol of motherhood and divinity for the Hindus. Therefore they worship cows. They don't eat cows, instead they drink milk, use the ox to plow the land, use the manure to treat the soil. The ancient Hindus saw a lot of benefits of not eating cows. They could other animals for food, however, alive cows provided more benefits then eating cows.
Beef is not banned in India, however, socially and culturally selling and eating beef is now allowed in the northern India, where as in the southern India beef is commonly sold in meat shops and restaurants.
Hindus abstain from eating beef because for the cows are animal form of Goddess Laxmi.