The answer to the query, why are we here exists in Indian in scriptures like Bhagavad Gita and also Upanishads (independent spiritual treatises).
We as human beings exist due to world of souls atmans, the consciousness existing in our heart. It is this spirit, soul atman within that manifested human form to work out its karma, dissolve dross impurities within forever.
The human form is only a medium for soul atman within to purify itself. It had no other purpose. Our soul atman is the absolute master and controller of human body all the time.
When Brahman, God Almighty exploded self with a big bang all pure souls atmans scattered all over cosmos at unimaginable speeds. In the melee, hurtling souls’ atmans gathered impurities.
To cleanse self of dross impurities within hurtling souls atmans manifest bodies after another when life supporting planets like mother earth evolved in cosmic system!
After manifesting a chain of 7.3 million bodies in insect, plant and animal life the soul atman within finally manifests the human form for the first time. Ever since souls’ atmans started their cosmic sojourn they desire regaining their lost original pure prime pristine primordial form at the earliest.
As human form is the highest manifest stage in cosmic life cycle, it is only in human form a soul atman finally liberates sell from cycle of birth and death forever. This became possible when human beings indulged in spirituality to reach state of enlightenment followed by moksha salvation. Indulging in spirituality detailed in Bhagavad Gita one finally becomes a Mahavira, Gautama Buddha Jesus Christ or Prophet Mohammed, an enlightened one.