I would add, if I may...
If a man believes in the supernatural, he will account for phenomena by the supernatural. We know that formerly just about everything was accounted for in this way. The more ignorant man is and at odds with his environment and the less control he feels he has over it, the greater his belief in unseen superstitious/supernatural powers. For instance, an altar or shrine or a memorial has been erected to the ‘spirit of the place’. For all we know, this may have simply been that on some occasion a person coming home drunk one night was frightened out of his wits by a barn owl he couldn't see clearly. Consequently the place attracted a reputation for being haunted and the altar was put up to placate the ghost of the ‘dead person’ who swooped from out of nowhere trying to take possession of the drunkard.
You open a humungous can/s of worms in the excellent OP, Tank. I will however confine myself as best I can to the gist of it.
Consider the early human, who subsisted on roots, plants and animals that could be killed with a simple club or stone and yet could kill him equally as well. Countless objects of terror surround our early ancestors. They stand next to rivers with no beginning or end, by bodies of water with one shore that feeds them and yet sometimes flood them out. There are beasts mightier than they. They suffer strange sicknesses. He is afraid of the sound of thunder, blinded by the lightning, and he hides from the growing black and menacing sky. Then, somewhere, sometime, a early human begged for the protection of the Unknown.
In the long dawn of humanity's awakening, the seeds of superstition were sown in the mind of man. How this happened, we do not know. But we do know the early humans thoroughly believed that everything happened in reference to them. He believed that by his actions he could anger or placate the wrath of the Unseen. Sometime along that long early road, he resorted to flattery and prayer and sacrifice to the unseen. Put in stone, bone or carved in wood, his idea of his God(s) and before long, he built an altar, then a hut, a hovel, a shrine and at last, a cathedral for these entities. Before these images he bowed and prayed, and at these shrines, he lavished his wealth, and sought, perhaps not eternal in the beginning, but nevertheless protection for himself and for the ones he loved.
And he made others believe as he did.
The few took advantage of the many and the few pretended or were deluded enough to eventually become intercessors between the helpless multitude and the Gods.
But why God? All religions report numerous and equally credible miracles. As Hume noted, the religions of the world have established themselves upon their miracles. Vanity, delusion, greed and zealotry have led to more than one ‘pious fraud’ supporting a holy and meritorious cause with gross embellishments and outright lies about witnessing miraculous events (Hume).
Testimony (a constant) depends on the intelligence and integrity of the testifier and the intelligence of the one who hears it. People, with the best of intentions, honestly bear false witness because they have been imposed upon by appearances, ignorance, vanity, greed and power hungry and are victims of delusion and illusion and their credulity, in many cases, believes everything except the truth. Another constant, and rather uniform in its sinisterness is the willingness of people at all times in all ages to desire wondrous events. They are more than willing to be deluded about them, to fabricate, create, embellish, enhance, and come to believe in the absolute truth of their own or others passions and heated over-imaginations.
The writers of the Synoptic Gospels tell us that Jesus set great value by marvels that no one is able to do today. Ministers cannot cast out devils, move mountains, wither fig trees, and they are affected by poison the same as any other. The writers of Jesus had a primitive idea of the value of magic. Did Jesus do the miraculous or have the writers sought to deceive the gullible, or, as is more likely, were over-credulous? It is important to remember that Jesus stressed the value of enchantment and advised his successors to conjure in his name. If the miraculous had not been connected with Jesus, it is most probable that he never would have been heard of. His ethical teachings alone would not have won for him the exalted position that has come from the stories of his miraculous birth, life and ascension.
Still I haven't answered "Why God?" and I may never answer it fully or to anyone's satisfaction. Yet, way way back, when reading and writing were unknown and history was hearsay handed down for generations, fragments of facts were taken for the whole, and the deductions drawn were sometimes honest...and...virtually nothing but the untruth was retold. Only the wonderful, the fantastic and the miraculous were kept. The more miraculous the story was, the greater the interest was generated. Storytellers and listeners were alike ignorant and alike honest. Way back then, nothing was known or suspected of the orderly course of nature because everything was at the mercy of a being, or entities, which were, ironically, controlled by the same passions that dominated the ancient man.
That is "Why God?", in part, way back then. It has only become more perverse in the last 1700 years.