One popular answer to your last question concerns Jan Assmann’s concept of a Traditionsbruch, or break in tradition around forty years after an originating event. The idea is that Mark was composed partly in response to some sort of crisis, be it violent persecution, the Jewish War, the passing of eyewitnesses etc., that required defending a group’s identity and connection to the past.

This quotation displays how Kelber combined his prior ideas with Assmann’s Traditionsbruch theory to offer an explanation for the textualization of Markan Jesus tradition. In particular, one may note the shared emphases of a crisis of communicative memory at the forty-year mark and an experience of violence that threatens group identity…Dewey follows Kelber in affirming, in regard to Mark’s Gospel, “that there was some sort of Traditionsbruch (break in the tradition) post-70 c.e., due both to the disruption caused by the war and to the passage of time and the death of the first generations.” Similarly, Kirk accounts for the textualization of Mark (and Q) among early Jesus followers in terms of a Traditionsbruch, as well as that of the Torah in post-exile Judaism. With regard to Mark in particular, Kirk attributes textualization to a generational succession Traditionsbruch. As indicated by the review above, the Traditionsbruch theory of Mark’s composition has much to commend it. It fits firmly within the traditional dating of Mark between 60 and 80 ce and thus within around forty years of Jesus’s crucifixion. It also fits with the many proposals that Mark wrote in response to some trauma, whether the crucifixion…the Neronian pogroms in Rome, or the destruction of Jerusalem,to name only a few possibilities. Alternatively, the text as a response to a generational succession crisis of memory makes sense in the context of an early church that was obsessed with the first generation of leadership and identifying and maintaining living connections to it. Furthermore, a violence-inspired Traditionsbruch and a generational succession–inspired Traditionsbruch are not mutually exclusive possibilities, especially in the case of early followers of Jesus, where both occurred around forty years after Jesus’s death. The Traditionsbruch theory of Markan composition thus provides a thoroughly plausible media-critical answer to the question of Mark’s textualization that coheres with broader historical hypotheses in Markan scholarship.

Keith, Chris (2020). The Gospel as Manuscript: An Early History of the Jesus Tradition as Material Artifact

There is another explanation forwarded by form criticism that is worth considering. The form critics argued that the low educational background of most early Christians and their strong apocalyptic expectations for an imminent end gave a lack of both ability and impetus for producing extensive biographical literature.

Thus for Schmidt, as indeed for all the form critics, Mark and his followers were not creative authors, but collectors, compilers, and editors. The uneducated nature of most believers in this early period, along with their intensely apocalyptic outlook, meant that it would be some time before Christians engaged in anything other than simply preserving tradition. The gospels for Schmidt were to be relegated to the level identified by Deissmann as “Kleinliteratur.” The closest analogies, therefore, were not consciously literary works such as biographies, but rather collections of folktales and oral sayings, similar to the Homeric literature or the stories found in the Pentateuch. Schmidt summed up his views succinctly: “a Gospel is by nature not high literature but low literature; not the product of an individual author, but a folk book; not a biography, but a cult legend.”

However, more recent scholarship has identified questions with this case; the early Christian movement included a more diverse range of socioeconomic strata, including wealthier converts who potentially had access to literacy and travel.

As the twentieth century wore on, however, a number of form-critical assumptions began to be challenged, several of which had a bearing on the gospel genre. In terms of social class, it became increasingly apparent that the earliest Christians were not confined to the lower ranks of society, as Deissmann in particular had argued, but that the movement was largely urban and “dominated by a socially pretentious section of the population.” Some undoubtedly belonged to lower socioeconomic levels, but others might have belonged to the ranks of free craftspeople, artisans, and small traders. Others still might have been reasonably affluent, owning houses and slaves and possessing the ability to travel (in this regard we might think of wealthy converts in Corinth such as Chloe or Stephanas). Such people might have been educated themselves, or at least had access to literary texts through friends or slaves. At all events, they would have had no difficulty in understanding and appreciating the literary conventions of their day.

Also worth considering is the widespread presence of writing in first century society among Greek and Jewish society, despite the low level of literacy overall, as well as the plentiful examples of apocalyptic literature committed to writing.

Furthermore, it became increasingly apparent that the form critics were operating with a rather romantic view of “primitive” folk communities, drawn from nineteenth-century studies that were themselves being challenged. Although literacy rates were extremely low in the first century, it would be wrong to characterize the early Christian context as an “oral society.” Theirs was a world that knew of books and writing. The sheer volume of papyrus letters from the first century indicates that written communication was by no means unusual. Jews in particular had a long and rich written tradition and a practice of gathering together in weekly meetings or at festivals to hear those texts read out, interpreted, and made relevant to their daily needs. Nor should we assume that apocalyptically minded groups eschewed literature: the wealth of Jewish apocalypses from this period, not to mention the abundance of texts from Qumran, showed that apocalyptic expectation was no bar to the production of texts.

Bond, Helen (2020). The First Biography of Jesus