Of course the larger question is why India in general chose more than 1000 years of illiteracy, when the Indus Valley Civilization that they conquered had a script, which they surely knew of. First-cousin Hittites, who left the Caucasus area at approximately the same time as the Aryans, c. 2000BCE, quickly began using Sumerian cuneiform when they entered the Middle East.
By the Buddha's time scripts were widespread, and sutras attest that the Buddha himself knew the Brahmi script that was in development at the time. Ashoka's inscription were in Brahmi and Kharosthi Prakrit, plus Greek and Aramaic languages. Still it was more than 200 years until the Pali Canon was finally written down.
Why did Buddhism choose illiteracy? So that the sangha would have a job memorizing sutras? Did they think that literacy was a defilement of some sort? Or is Buddhism just innately conservative? Ideas appreciated...
A Tradition of Experience
Buddhism is a tradition of experiences and not emphasized as written tradition.
As Buddhism is non dogmatic. Oral tradition or experience tradition to understand true liberation and beyond.
Buddhism as Open Doctrine
I agree that Buddhism is an open doctrine, maybe better described as a dialectic, an articulated back-and-forth discussion or debate of the salient points at its foundation, but that does not preclude the use of writing as a tool of development. Of course, they DID write it down, c.20BCE as the Pali Canon, but why did they wait 500 years?
And by then, of course, Mahayana was being created, and not accidentally as a 'cult of the book'--about time, since Greek philosophy was past its classic age by then (and maybe a causative factor for Mahayana, since Greeks and Buddhists mixed and mingled heavily at the Abhidharma 'stomping grounds' in Gandhara).
Of course, Indian Buddhists weren't alone in this, as the Vedas weren't written, either, and for even longer, though alphabets existed for that purpose at that time 1500-1300BC. In fact the culture the Vedic Aryans supplanted, the Indus Valley Civilization, had its own alphabet, which may have been a disincentive, since they were typically seen as 'slaves' by the chariot-driving Aryans. So the only written attestation we have of that era of proto-Sanskrit is from the Mideast Mittani dynasty and its mercenary Aryans.
Now it's no question that the Aryans and their Brahmin descendants were inherently racist, with a caste system to prove it, but are Buddhists inherently conservative, resistant to change, even when it would advance the spread of the Dharma? Or did they resist so that the Sangha would have a reason to exist? That was their main job in the early days, the endless remembering and repetition and recitation of sutras.
Buddhism seems to have no qualms about embracing the Internet, or Facebook, and this forum is proof of that. But that's more of a Western thing. Is Asia inherently conservative? And is the current Western infatuation with Buddhism good for the spread of the Dharma? I guess time will tell...
buddha's death
Before one has a say about when the canon started to coalesce or why, it would prove useful to determine the period the historical Buddha might have lived in.
949 BCE, 881 BCE, 486 BCE, 368 BCE1, are all dates different authentic Buddhist traditions present as the 'historical' date of Gautama Buddha's death. In 1799, in a volume of scholarly Asiatic Researches, Abu'lfazi's – a Muslim traveler under Akhbar- account is mentioned, which situated Buddha's birth in the year 1366 BCE: the myth ought to have become fact.
That is not mere trifle. 949 BCE as date of the Buddha's death was instrumental in the doctrine of many important Japanese denominations coalescing in the Kamakura period (1185-1333). Leaders of the new sects could claim -just as their Chinese VI century Tiantai predecessors - to be the savior of people living the the Age Of Degeneration of doctrine Mahayana texts posited 2.000 years after the Buddha's passing.
A cursory exam of popular Google Books reveals countless possible dates for Buddha's death proposed in research: 623 BCE2, 544 BCE, 487 BCE, 483 BCE, 477 BCE, 468 BCE, 384 BCE... In the Christian canon coming from supposed eye-witness testimonies, Jesus is crucified either after noon the day before Passover (John 14:16;18:28); or mid-morning the day after Passover (Mark 14:12;15:25).
Irenaeus might have had clues, for (John 8:57) the Gospel recites:”"You [=Jesus] are not yet fifty years old," they said to him, "and you have seen Abraham!"”. A Jesus who's almost 50 surely would have died in Claudius' reign (41-54 CE), or even later. Irenaeus (Against Heresies, ch. XXII) unambiguously writes:”but from the fortieth and fiftieth year a man begins to decline towards old age, which our Lord possessed while [Jesus] still fulfilled the office of a Teacher, even as the Gospel and all the elders testify; those who were conversant in Asia with John, the disciple of the Lord, [affirming] that John conveyed to them that information. And he remained among them up to the times of Trajan. [emperor 98-117 CE] ”.
Whether this series of disparate dates looks like fact rather than myth is left to readers to consider3:
FWIW
The Importance of Dates and Details, and Writing
I'd say that this what happens when writing is eschewed in favor of oral tradition. I suspect the reason for this was the fear that writing would supplant our ability to think, and in effect, take over the thought process. What they failed to realize, though, in my opinion, is that that has already happened, with the adoption of language, regardless of whether it is written or not. Once we adopt language, we think in language, and the ability to revert to non-narrative thought can only be approximated in meditation, or something similar.