Think of it this way,
Matthew - the Jews who needed proof that Jesus was the promised Messiah, which explains the numerous references to OT prophecies that Jesus fulfilled.
Mark - the Christians of Rome who were suffering under Nero’s persecutions. They needed to know that it was in suffering for Jesus that they would achieve their glory, that they weren’t suffering in vain.
Luke - the Gentiles. Luke has to explain the meaning behind numerous Jewish-isms.
John - Those that wanted to know Jesus even better than they had by reading the Synoptic Gospels (Matt, Mark & Luke). John established the fact that Jesus, the One closest to God is the One who reveals him in chapter 1 - “No one has ever seen God. The only Son, God, who is at the Father’s side, has revealed him.” And then shows that he is the one, at Jesus’ side, who will reveal the True Jesus in chapter 13 - One of his disciples, the one whom Jesus loved, was reclining at Jesus’ side**.**