incidentally, I learned this the qother day, and it explains things a bit
wiki
"The Q source (also called Q document, Q Gospel, or Q from German: Quelle, meaning "source") is a hypothetical written collection of primarily Jesus' sayings (logia). Q is part of the common material found in the Gospels of Matthew and Luke but not in the Gospel of Mark. According to this hypothesis, this material was drawn from the early Church's oral tradition.[1][2][3]
Along with Marcan priority, Q was hypothesized by 1900, and is one of the foundations of most modern gospel scholarship."