I think this is because the Scriptures were widely recognized from the beginning. It was only when large movements developed that written declarations of what comprised Scripture were made. For example, confronted with a growing gnosticism St. Athansius made a written declaration of what the canon was as the bishop in Alexandria.
Another example is the Muratonian Fragment which dates back to 170 AD. It follows the Marcion movement.
Sometimes in the rush to take credit for something we fail to recognize how seriously Christians of the Apostolic Era and the century immediately following considered these matters. They knew who the Apostles were and they knew who traveled with them. They were pretty quick to discredit writings of "recent appearance", "questionable authorship" or that were not "God Breathed".
“They knew who the Apostles were and they knew who traveled with them. They were pretty quick to discredit writings of “recent appearance”, “questionable authorship” or that were not “God Breathed”.”
As a general proposition, I think you are right, but its important to remember writings like Barnabus, The Shepherd and the Clementine Letters just as it is important to recognize why, say, The Shepherd was rejected ultimately as compared to why the Gospel of Thomas or that of Judas were rejected or how Hebrews and Revelations came to be part of what we have as the canon of the NT today.