For the simple reason that Hindutva is not a religious movement. It is a cultural one.
It might come as a surprise to many people who have gotten used to seeing Hindutva proponents described as “religious fanatics”, but the Hindutva movement actually has more to do with culture than religion.
Hinduism is described as a religion by many. Many others say that it is not a religion and is, in fact, a “way of life”. The way the conversation about religion has been had in recent decades has turned present-day cultural discourse into a soup of labels and assumptions. The reason is that patently non-Indian categories are being used to classify Indian cultural phenomena. This atheism / theism / fanaticism confusion is just one case in point.
Vinayak Damodar Savarkar, when he was young, was as moved by the Indian freedom movement as any other young man his age. And like many Indians back then (and even now) he had opinions about the society he lived in as well. Like everyone else, he focused his efforts towards achievement of a singular goal — a free India.
The goal of a free India has nothing to do with religion. It never has. What it does have to do with is a cultural construct. In order for India to be free, it was important for freedom fighters to believe in an ideal. In Mohandas Gandhi’s case, this ideal took the form of a country that had the village as the seat of power and he used religion and god as motivating elements. Nehru similarly, used a vision of a scientific and peaceful nation as his ideal.
Savarkar’s ideal was rooted in the culture he belonged to. And that too, a sanitised and cleaned up version. He did not believe in a higher power the way most Abrahamic religions describe it. He did not believe in the philosophical constructs that formed the foundations of popular Hinduism — Karma, reincarnation, and bhakti etc.
Savarkar’s Hindutva was based on the cultural unity of the Indian sub-continent. The foundation of his ideal was that which, in his view, all Indians shared. In his view, god played no part in forming this ideal.