That is a very good question. It all has to do with a bishop who put the church on the wrong foot very early in Christian history.
Papias and his views
In ca. 135 AD, bishop Papias of Hierapolis (Asia) wrote a work “Explications of the Words of the Lord”, in five books, which are lost now apart from some quotes.
Papias received his knowledge from those who had heard the apostles, he said. It is clear that he introduced the oral tradition as a source for biblical knowledge, instead of what the Bible says about this.
Papias also claimed that Matthew wrote the words of Jesus in Hebrew and the other gospel writers would have used this Hebrew source to write the Greek Gospels. Apart from an oral tradition he also introduced the idea that “the Words of the Lord” would not exist anymore in their original form, but only in translation (in the Gospels).
On The Wrong Foot
The suggestions of Papias had a great impact throughout history. Even now it is generally accepted in theology that Jesus’s words in the Gospels would have been transmitted in the first place by oral tradition and they would have been translated from Aramaic into Greek during the period of the oral tradition. But where is the Biblical evidence? Oh yes, mistranslations enough.
Captivated by Papias
The vision of Papias included two things: oral tradition and a theory about the language of Jesus. It sounded intelligent and pious, but it was a disaster. These theories actually said that the original words of Jesus (in Hebrew as Papias supposed) would have been lost, as we possess the Gospels in Greek.
In the course of time, not all theologians agreed with Papias’s opinions, nevertheless he had infected them with his wrong presuppositions, that continued to have their impact.
Dark and Hurtful
Willingly or unwillingly, theologians felt compelled to follow the tradition settled by Papias: (1) the theory of the oral tradition as a source for the Gospels, and (2) translation of Jesus’s words in an early stage. Today the supposed language of Jesus is Aramaic (instead of Greek). Consequently the theological result would be: the original words of Jesus are lost. Beyond doubt we are confronted here with dark and hurtful theological failures. How do we get out of this stranglehold?
“1Inasmuch as many have undertaken to compile an account of the things accomplished among us, 2 just as they were handed down to us by those who from the beginning were eyewitnesses and [being] servants of the word, 3 it seemed fitting for me as well, having investigated everything carefully from the beginning, to write it out for you in consecutive order, most excellent Theophilus.” (NASB)
Role of The Bystanders
In the first words of his Gospel, Luke speaks about “the things accomplished among us”. Nobody is in doubt that these things are the Jesus events (Acts 1:1), and consequently us are the bystanders, those who were there, the spectators.
Also in v. 2 it is about us: information about the events transmitted to us. This second us is again the bystanders, as it is not permitted to change the reference word us mid-sentence. In short, information about the events of Jesus had been delivered immediately thereafter unto the bystanders.
Many of the bystanders compiled narratives, and their work were in writing. We know that, as Luke followed later their example, just as he wrote in v. 3: it seemed fitting for me as well … to write … (v. 3).
Reports of The Eyewitnesses
The eyewitnesses delivered also being servants of the spoken word. They delivered during the spoken word, but not orally, as they would disturb the spoken word. Consequently they could only deliver in writing during the spoken word. They brought out reports for the bystanders (the public).
In the blessed atmosphere of Jesus’s presence each was willing to share the information to others to create their own narrative. Back home, many were able to read and tell at home about what had happened.