Blackwell said
The appearance of the first gospel, by Mark, shortly after the Jewish revolt from 66 to 73CE is probably more than just coincidence.  The loss of life in the conflict was appalling with estimates of more than one million killed, climaxing with the destruction of the Temple and razing of Jerusalem in 70CE. Those who could flee became refugees in Egypt, Syria and other places where they set up exile communities so one reason for writing the gospels might have been to demonstrate that Paul’s new “improved version” of Judaism was the way forward. The mythicist claim is that Jesus did not exist and Mark made up the whole story but, if Jesus did exist and Mark got oral information from refugees, he may have wanted to record it before it was forgotten. One intriguing possibility is that Jesus had sympathizers among the literate elite in Jerusalem, who made records while he was alive, and these documents were kept secret after his crucifixion until they were taken into exile and became available for copying.  

I think many factors contributed to the production of written gospels.

There were quite a few proto-christian communities around the Mediterranean  long before Jewish revolt. If we assume that they were “apocalyptic”, that is, expecting the end of the present world and the return of the Lord, they may have seen the revolt as the beginning of the birth pangs.  But already at the time of Mark, they must have realized that they were going for the long haul, in which there was a need for organization and written documents for the transfer of the culture to next generation. As mreichert notes, in the initial stages of Christianity, illiteracy prevailed. Also apocalyptic fervor dominated, making written documents less important.

Blackwell said
gavriel said

I agree that those who expected the world to end any day saw no point in making records. However, judging from Paul’s epistles, people in these proto-christian communities knew very little about the details of Jesus’s life anyway so it is doubtful if the gospel writers got much information from them.  

Paul obviously don’t know much about we know from the written, canonical gospels, and it is therefore reasonable to think that the communities he founded, initially knew just some few facts, besides Paul’s peculiar theology. But the canonical gospel material must have had a long oral pre-history originating from other people than Paul, and ultimately the traditions got mixed, throughout all types of communities. For instance many scholars think that Mark is influenced by Pauline theology.

Blackwell said

gavriel said
Paul obviously don’t know much about we know from the written, canonical gospels, and it is therefore reasonable to think that the communities he founded, initially knew just some few facts, besides Paul’s peculiar theology. But the canonical gospel material must have had a long oral pre-history originating from other people than Paul, and ultimately the traditions got mixed, throughout all types of communities. For instance many scholars think that Mark is influenced by Pauline theology. 

Why did Paul not refer to oral pre-history originating from other people? Maybe because it was confined to the Nazoreans under  James in Jerusalem, with whom Paul and his followers had limited contact until the Jewish revolt forced them out.  

Paul gives some few important formulas, that he has not concocted himself. But it would have been impossible for him to excel in stories about Jesus, at a time when Jesus’ closest disciples knew far more. That would have made him inferior to those other apostles. Paul very much wanted to be another apostle on the level of  Peter,John and James, and not an ordinary disciple, subject to those. So he is excelling in high-brow theology, something that the “super apostles” could not.