Why do Indians(Hindus) follow God though most of them haven't read holy books like Geeta? I have seen them blindly following the god just because of religious reasons. Why so?
Why do most of the Indians (Hindus) eat rice though they haven't known how it is grown?
Why do most of the Indians (Hindus) drive car though they haven't taken a tour of the factory which explains how a car is manufactured?
If one answers this, they can easily understand your question also. It is not mandatory to read books to believe in God. Both are mutually exclusive.
Faith is a matter of belief that God exists. To believe there is a super power which helps us when we struggling. To believe that an entity exists when you are helpless. He helps us when there is no one else to help you. Beliefs can form due to many reasons. There is no compulsion that one should read Bhagavad Gita or Ramayana or any other scripture. As you mention Indians, they tend to know about Hinduism and god culturally without reading any holy books. This is not a blind belief.
Most of the people in this world who believe in God perform prayer in one or the other way and ask god to solve their problems or ask for their welfare. You need not to be qualified or you have to study some holy book to ask God to request him to solve your problems. Reading book is only one of the many ways to realize the existence of God. Experiences that God exists and helping you is one of the main reasons one forms a belief. There is a story in Bhagavatam about an elephant which fought with a crocodile. It failed to rescue himself and started praying Lord Vishnu. Apparently, the elephant did not read Bhagavad Gita. It only knew that God exists and helps when there is problem. Following are some of the words that elephant says. (Taken from Potana Andhra Mahabhagavatam and English translation from wikimedia commons PDF.)
Evvaniche janinchu jagamevvani lopanundu leenamai
evvaniyandundindu barameswarudevvadu mulakaranam
bevvadanaadi madhyalayudevvadu sarvamudanainava
devvadu vaninaathma bhavuneeswarune saranambu vededhan
By whom this world is created, by whom it is maintained, in whom it will be dissolved and who is the Lord of the creation and its root cause, who is the spectator of the beginning, being and ending of these worlds, who encompasses everything, who is self sustaining and sustainer of all, to that Lord, I pray for my rescue!
Lavokkintayu ledu dhairyamu vilolambayye branamulun
tavul dappenu murchavachhe danuvun dassen sramambayyedin
neeve tappa nitah paramberuga mannipandagun deenunin
rave eeswara kavave varada samrakshinchu bhadratmaka
Oh Lord! I am not left with an iota of strength, my courage is shaken ,my life is in danger ,I lose my consciousness ,my body is tired, all my energy is spent, I feel fatigue, now, I don't know anything except you, forgive me, I am totally helpless . Oh, Lord! I request you, implore you to come and save me!
You are the embodiment of strength and Grace. You are the only refuge for my rescue
kalaDaMduru deenula yeDa
kalaDaMduru bhakta yOgi gaNamula pAlaM
kalaDu kalaMDaneDu vaaDu kalaDO lEDO
Wise men say that He is available for the people in distress and favorable for saints and sages and He is present in all places and directions! I call upon such Lord to take pity on me but does he exist? If he exists why he is not coming to save me
Finally, Lord Vishnu arrived and saved the elephant. No discrimination was shown that it didn't read some book or it is an animal. Every creature is dear to him if it prays with love and affection.
These incidents are another reason people believe in God. This is not something which is formed due to no reason. We just don't know the strong reason for the belief when we observe it from outside and tend to term it as blind belief.
God says in the Gita (Chapter 7, sloka 16):
..four classes of people of virtuous deeds adore Me: the afflicted, the seeker of Knowledge, the seeker of wealth[any material gain] and the man of Knowledge.(Translation by Swami Gambhirananda)
So He Himself makes it clear who worships Him and why.
Bhakti is the only thing that pleases Him. He never said that for following Him, reading of Gita or any other book is obligatory.
Knowledge of the holy books is not required to believe in God. Long before a Hindu child is able to read the scriptures, the customs and legends are inculcated in him by his family, parents and relatives. By the time he is old enough to use his knowledge and intelligence, his psyche has already been affected by all these.