The Quraish tribe were well known as illiterate people (ummy people). They relied on their memorization.
The Quranic canon is the form of the Quran as recited and written in which it is religiously binding for the Muslim community. This canonical corpus is closed and fixed in the sense that nothing in the Quran can be changed or modified. The process of canonization ended under the third caliph,
Uthman ibn Affan (r. 23/644–35/655), which was about twenty years after the death of Prophet Muhammad.
[38]
By the time of Uthman's caliphate, there was a perceived need for clarification of Quran reading. The Caliphate had grown considerably, expanding into Iraq, Syria, Egypt, and Iran, bringing into Islam's fold many new converts from various cultures with varying degrees of isolation.
[39] These converts spoke a variety of languages but were not well learned in Arabic, and so Uthman felt it was important to standardize the written text of the Quran into one specific Arabic dialect. Another reason for compiling the Quran was that many Muslims who had memorised the Quran in its entirety (
huffaz) were dying, especially in battle.[
citation needed]
(WIKIPEDIA)