Why is a religion-less society a myth?

 Why religion is integral part of almost all culture?

I recently fell ill with a fever and, with nothing else to do, started playing mobile games. There I realised the importance of rules. Just like players in game, the life of an actual human being is very trivial. It is hard to admit fact that vast majority of people (almost everyone) will not have any impact on anything apart from influencing population which is consisted of trivial humans. The evolution of human has selected our species based on survival instinct which include unjustifiable admiration of continuance i.e. timelessness. Eternity might be an actual concept of cosmos but for some reason humans are now bothered by this. They eagerly want to be part of that eternity but age puts hard limit to this desire. Now the best way to achieve this is by being part of an old system that is perpetually running for centuries earlier by ancestors and now by ourselves. The archaic tradition and customs are soul for this old system. But the issue of continuance arises when rational brain starts altering those norms. To avoid this a robust system needed to be developed which could put an end to all the questions related to tradition and customs passed down through generations. This essentially prevents ancient and ripped knowledge and know-how to be lost by the people who weigh their relevancy to their historic importance without properly understanding that once it's out of use, it will be out of the history thus causing humans to lose their purpose to be part of "eternity". 

This idea of abiding by the "ancient law" acts as glue to hold the society togather. The belief in old customs is a skeleton for a society with unified power much more capable than individual potentials. This belief system provides a sense of belongingness among contemporary humans bound by shared way of life. Biologically humans are social animals and hence being religious ironically makes this choice rational.