Atheism is disbelief in a personal God. It is not very popular in India, despite the various ploys of inroad it has attempted throughout history.
There are various kinds of atheisms in India. Some of these are dead, as far as systems are concerned; others live in compliant modes. For instance, charvaka atheism died away as a system, but yoga, samkhya, and Vedanta took accommodative modes.
The six heterodox schools (Charvaka, Jainism, and 4 schools of Buddhism) were labelled nastik or non-believing because they rejected the Vedas. However, these also have no place for the Supreme Personal God in their systems. Jainism considers a plurality of spirits to be eternal, and matter to be evil. Buddhism considers the human spirit as an aggregate of the 5 skandhas; in fact, it disbelieves the spirit as being real according to the doctrine of anatta.
Samkhya looks at Purusha and Prakriti as the eternal principles in a form of dualism. Vedanta regards the spirit as all that is and the one without an other (non-dualism); everything else is a delusion; thus, only the self eternally exists according to it. God, as the wholly other, doesn't exist.
However, neither the popular Hindu nor the tribal, following his various belief-systems, is willing to accept such atheistic doctrines. Thus, some sort of worship is vital in popular Jainism, Buddhism, and Hinduism. Of course, magic has made some inroads as well, quite contradictorily to the concept of theism (Theism can't allow any power apart from God nor able to supersede God, since God, by definition, is the Supreme One).
There are a few antisupernaturalists who regard science as the enemy of the concept of God and of creation. But, their impact doesn't seem to be as strong among the 4/14 Window group who have already formed faith before entering High School. We don't count godless lifestyles here. It is possible that one believes in the supernatural and still lives a godless life. The demons do - they believe in God and yet are godless.
We also don't mean that most Indians are monotheists. We only mean they are not atheists. Atheism is too tasteless for them; and quite impractical as far as philosophy of life is concerned. Atheism has no inspiring story to tell.