Hinduism primarily is recognized by its scriptures Vedas (Hinduism revelations), Upanishads (independent spiritual treatises) and sermon of Bhagavad Gita by Lord Krishna.
All the three series of scriptures were so intense on the scales of jnana wisdom that even scholars find it difficult to assimilate their teachings.
All the spiritual teachings of Hinduism were beyond capture of science and the common man. Bhagavad Gita and Upanishads relate to spiritual science assimilating reach human beings successfully reached state of enlightenment in their lifetime.
How difficult it is to understand teachings contained in Bhagavad Gita and Upanishads can be gauged from the fact that in last about 150 years amongst 7 billion people existing world over only Sri Ramakrishna Paramhansa and Maharshi Ramana succeeded in reaching God.
As nothing in Bhagavad Gita and Upanishads could be understood literally, it was beyond reach of most worldwide including Hindus.
As wisdom of Hinduism scriptures was beyond reach of mankind, it remained confined mostly to India only. No matter how much time passes, this situation is not going to change. Only an ardent seeker like Swami Vivekananda finally succeeds in understanding spirituality as in Bhagavad Gita.
The minimum standard required to indulge in Hinduism scriptures is level of Swami Vivekananda. One needs becoming a Swami Vivekananda in real life to understand Bhagavad Gita. Anything less would not do. How many people in this world were competent to become a Swami Vivekananda in real life!
For mankind to reach state of enlightenment, indulgence in Bhagavad Gita was an absolute must.
Even Jesus Christ during his missing years (age 14 to 29) came to India to indulge in sacred texts like Bhagavad Gita, Upanishads even Vedas. During times of Jesus Christ both Taxila and Nalanda Universities were great places of learning.
In present times the original text of Bhagavad Gita containing 700 shlokas verses in Sanskrit with English transliteration is available for mere $1 from Gita press, Gorakhpur, India but there were hardly any takers. Reason being, one can understand gist of Bhagavad Gita only through contemplation (chintan) never literally.
Mastering delicate art of contemplation is a must to reach the hidden underlying meaning of sacred texts contained in Bhagavad Gita and Upanishads.
Even in India people preferred following religious practices (rituals) compared to spirituality whereas Bhagavad Gita is all about indulgence in spirituality to reach the spirit existing within.
The spiritual Hinduism scriptures were all about taking the inner journey towards our soul atman existing in heart. For human beings to realize self, become a pure soul atman travelling path of jnana yoga (absolute wisdom) as detailed in Bhagavad Gita is necessitated.
Everything related to Indian spirituality seems difficult to mankind, prime reason why there were no takers.