Why does John omit the institution narrative if John 6 teaches the Eucharist?

John writes later, presuming the Synoptics’ historical account. He expands the theology rather than repeat narrative details. John 6 provides the doctrinal depth. The absence of repetition does not negate the institution; it reflects Johannine purpose. See extended commentary on John for parallels where John presumes Synoptic material and develops the theology.