Michael J. Kok, The Gospel on the Margins: The Reception of Mark in the Second Century (Minneapolis, MN: Fortress Press, 2015), 9-10, 11.
Evidently the weight of Petrine authority did not compel an active readership of Mark. The reason for this limited use may lie in Mark’s glaring absences. Elements missing included the lofty Christological language of John, the ethical guidelines of the Sermon on the Mount or Plain, or the popular infancy or resurrection stories. Scribes felt compelled to amend Mark’s text, tampering with its conclusion and perhaps introduction that they held to be unsatisfactory. The perception of major holes at the beginning, middle, or ending of Mark’s story may have encouraged the production of new narrative lives of Jesus….
Given Mark’s lackluster reception in the patristic period, it is astounding that it survived at all once its contents were almost completely reabsorbed in Matthew and Luke. It could have disappeared without a trace like the other Synoptic sources lost to the dust of antiquity (cf. Luke 1:1-3).