The birth of Krishna was for a very specific reason. When society reaches its lowest ebb, a point of no return then advents a messiah, savior, an avatar to place the society back on its pedestal.
In absence of an avatar per se Hinduism scriptures, the society could not recoup its energy.
Every 3500 to 5000 years life comes full circle on mother earth. This means every 3500 to 5000 years advents a messiah, savior, avatar to re-establish Dharma (righteousness) against evil forces of adharma (lawlessness) prevailing at that time.
As we can see from history birth of Krishna was not easy. He was the eighth child of Devaki and Vasudeva, the earlier seven children brutally killed by the real maternal uncle Kamsa.
Everything in field of spirituality is achieved after great sufferings, sacrifices. This was how God tested human beings for their future role.
In Dwapar Yuga advent Lord Krishna and in present times mankind would witness advent of Kalki Avatar, the annihilator of Kali Yuga. Between 2022 and 2025 would surface Kalki Avatar.
Such would be the might of this Kalki Avatar that 2000 million people world over would develop absolute faith in him. Another 2000 million people would firmly believe in him.
Kalki Avatar, a one-man army encompassing almost equivalent powers that of Krishna would be a phenomenon to watch. Kalki Avatar would also pass through great sufferings in life. That is how an avatar is born.
The sole aim of every Avatar is re-establishing Dharma (righteousness), bringing back order in the society.
Allegorically Krishna represents soul atman existing in all human beings. Every 100 to 200 years mankind witnesses surfacing of an enlightened one, so was ordained by god.
Imagine if 50 Gautama Buddha came simultaneously, whom to worship or not! Acting as a guide pillar to entire society world over an enlightened one disseminates the much-needed wisdom of Bhagavad Gita to humanity. To maintain order in the society this was much essential.
In the last about 150 years amongst 7 billion people existing world over Sri Ramakrishna Paramhansa and Maharshi Ramana finally succeeded in reaching state of enlightenment in their lifetime. Next would be Swami Vivekananda who refused gaining enlightenment in his lifetime.