Most people (probably more than 90%) of the people in Jesus’ era were functionally illiterate. The word “functionally” is important in this statement–they might be able to recognize key words in passages of the Torah, and hence be able to “read” the Torah, but that is a far cry from being able to read anything in writing, much less be able to write information down themselves.
As an example of what I mean here–my younger sister was able to “read” the poem “The Owl and the Pussycat” when she was about three years old. However, it must be noted that our mother had read this poem to us over and over again several times a week, with both of us looking over her shoulder as she read, using her finger to point to words as she read them. My sister could recognize the poem from the title alone in any book she found it in, just because of the words in the title. Because she had memorized the actual text of the poem, it was relatively easy for her to pretend to read that text when we went to our grandmother’s house, which had the same poem, but in a different book. However, she had a very hard time actually learning to read books on her own.
In the period and geographic area in which Jesus was supposed to live, only a very small percentage of the population was functionally literate, in the sense of being able to read new words in new contexts, much less be able to write down new sequences of words that weren’t copied from an existing text. Most of the functionally literate people were either wealthy people who were educated in the Roman system (where Greek was typically taught as THE literate language, like Paul), or they were Rabbis, who were the learned class of the Jewish society. Jesus could probably recognize words enough to identify the passages from the Torah that he had heard often, but that is hardly the same as being functionally literate. (Based on the New Testament, Jesus’ family was NOT wealthy, although it is possible that Joseph was part of the Pharisees (the class that operated the Temples and ordained the priests)).
Given the emphasis on oral–rather than written–traditions that existed 2000+ years ago, it would not be surprising to me that Jesus was functionally illiterate. Nor would I necessarily expect someone from that era to feel that it was necessary to put down in writing every event that occurred to him–just as I would not expect someone in 1990 to have a blog–yes, the technology existed (barely), but it was not prevalent.
In the long run, how many of your life’s precepts do you actually record?? From every verse in the Gospel, Jesus did not believe that he was more important than any of his disciples or followers. He felt he was simply the “son of Man,” who was supposed to pass on the Word of God. Nowhere in the Gospel does Jesus claim that he actually IS God, although this interpretation occurs elsewhere in the New Testament (most of which was written long after the crucifixion).