Why did Rabulla make his own Aramaic gospels?

[Dave]

in the Greek western tradition, when discussing the origin of the Synpotic Gospels, they claim that the original Gospel was that of Mark, and that Matthew was Mark, but expanded, because Matthew has similar readings to Mark. Some go as far as saying that the sayings of Jesus come from a lost text called Q.

Yes Keefa, one can surmise that Marks text was not completed. There is the probability of interpolations at the end of it (many have conjectured). It is possible that Mark was expanding on what Matthew skipped over and vice versa.