Or, to put it in historical context, between 1,500 and 5,000 years ago.
The answer, I suspect, may lie in the word "Dark".
So, say if 90% or so of people were illiterate and possessed the intelligence and wherewithal akin to present-day chimps, what does that make of present-day believers?
Are they just shaven chimps?
Depilated chimp descendants?
Or are they just plain lazy and unimaginative people with no mind of their own?
I believe the latter.
And prophets were conveniently created at a time when human rights were virtually non-existent. When women's importance in society ranked just bellow that of cattle (as in present-day Islam) and children were seen as a burden and vulnerable prey (as in present-day Catholic Institutions and Sharia Law).
Oh yes, it could only have happened back in the days. A time when gullibility reigned supreme. A time when the uneducated revered the few who could speak and write, and the eloquent were instantly deemed as divine.
In all, the Dark Ages were the perfect time to create Gods and Prophets. It simply couldn't happen today.
Can you image a news flash on BBC proclaiming "Important announcement, a Prophet has just emerged in the Middle-East village of Bethlehem, south of Jerusalem..."
It just wouldn't happen. And for a very good reason. We've come a long way since. At least some of us.
Now, in the Enlightened Era, prophets are used to generate profits...and war...and prejudice...and bigotry...and divisiveness...and suffering to name but a few, but at least no more are being invented.