Well, you know that they are called "parables." And if you were teaching something that could get you killed in any of several very nasty ways you might want to disguise that teaching as a story and let the hearers figure it out for themselves.

Just for grits and shins, here's a chronology of Christian scripture, with the dates supplied by the best scholarly techniques. I've put an asterisk (star, splat, *) by those which the scholars are certain of but for which we don't have physical copies.

50 - 70 CE

*Sayings Gospel Q
*First edition of Thomas
Gospel Oxyrhynchus 1224
*Signs gospel

70 -80 CE

Mark
Egerton Gospel

80 - 90 CE

Matthew
Luke

90 - 100 CE

John

100 - 150 CE

Gospel of Peter
Gospel of Mary
Secret Mark
Infancy Gospel of James
Infancy Gospel of Thomas
Secret James
The Amulet (Gospel Oxyrhynchus 840)
Dialogue of the Savior

150 CE and later

Gospel of the Ebionites
Gospel of the Hebrews
Gospel of the Nazoreans
Gospel of the Savior

(from "The Gospel of Jesus according to the Jesus Seminar" (Santa Rosa, CA: Polebridge Press, 1999).