In answer to the OP on why it took so long to identify with one true God… and this assumes we have already done so.
Lots of reasons:
First, not everybody is on the same page (separate cultures).
Next you have all these different guys, telling all these different stories, creating all these different beliefs, so we get all these different gods.
Then someone says, “this god is the only real god” and it (slowly) catches on.
Following is a short history (which I have posted before) concerning archeological evidence for the development of monotheism from polytheism (not all scholars agree this development was from polytheism - but it seems to be the strongest theory).
Now how this actually occurred is still debated among historians but most agree that the Israelites (and their God) were well aware of other gods, and even worshiped a few, (they were even allowed to you see, just not before God).
Ancient Hebrews probably picked up their early religion* from the Caananites who had a whole bunch o’ gods to choose from (they’d put the Romans to shame).
In some hypotheses, Al (El), the Caananite creator of heaven and earth, is adopted by early Israelites as their “God”. El, by the way, was not their (Caananite’s) chief god, that honor was given to Baal, El’s son. Baal also took El’s wife Asherah when he got that job (to the dismay of all the other gods it seems, but this is another story).
*According to The Encyclopedia of World History, sixth edition, edited by Peter N. Stearns (original editor, William L. Langer) the course of the monotheistic worship of Yahweh is problematic. And although they (Stearns et. al.) are careful to point out that there is still much debate over the issue of exactly how early on monotheism developed in the Hebrew religion, there is a 9th century Hebrew inscription that suggests Yahweh had a consort named… (drum roll please) Asherah. (this would strongly suggest the Caananite tie)
Centuries later, some upstarts came to challange the Jewish beliefs, and apparently some of these really caught on (one is still around today). 
Then it took another several hundred years to get to a popular fella called Muhammad.
Skip ahead to today, and we still have hundreds of different religions, all with their own histories…
Why did it take so long? 