To me it's just a mater of survival of the fittest (or the fit enough).
When homo sapiens lost a family member they cried and went on marching with grief in their hearts, leaving the deceased to rotten or be devoured by carrion eaters.
One "day" a combination of human traits lit on the notion that death wasn't the end of a person. That hardware would decay, but software would move on and change into a new state: the ancestors, depositary of old experience and forgotten deeds, who in turn became the guardians of the proto-tribal family. Religion had emerged.
Burying or cremating them was the way to mourn and show respect. Why went this on and became increasingly elaborated? Because it provided some adaptive edge. The society had evolved into one led by tradition, with the ancestors increasingly being spiritualized and empowered. Old rules that had guaranteed survival wouldn't be broken or forgotten so easily. Each individual's behaviour was no longer exclusively controlled by the mechanics of guilt, which had emerged long before to avoid murder and endogamy. Now, there were spirits watching over you, and they eventually not only saw your acts but read your soul.
As tribes, large tribes, cities, proto-societies emerged, these spiritual beings became more complex, more powerful, more arbitrary and more personal. Kings and gods were born at the same time, cast from the notion of both living chief and dead chief, together with a general motherly spirit representing nature.
It was obvious no much time would pass from the birth of large kingdoms, empires and some sort of international circulation of luxury goods, and later cultural progress, that the notion of few or even just one omnipotent syncretic god would emerge.
The rest is just Darwinian: lots would be willing to die for Allah and fewer to do it for Ahura Mazda then, guess what direction conversions followed and who's the most adored one nowadays? What about Arnaud Amalric and his "kill all of them, God will know his own"? How many Christians and how many Albigens are there today? Not always the last standing "god" is the better one. Aten was just an ephemeral development, but intriguingly enough, its discriminative nature could have served as a model for the ethnic only-god "Jehovah".
It's just Darwin. That's why "they" hate him so much.