Actually it is not.
Rejection of apostolic authorship led to severe questions about canonicity. Eusebius, bishop of Caesarea in the early fourth century, was apparently influenced by the work of Dionysius and suggested that the book was written by a John the Elder of whom Papias spoke. Others in the East who questioned the work include Cyril of Jerusalem (315–86), Chrysostom (347–407), and Theodoret (386–457). It was not included among the canonical books at the Council of Laodicea (ca. 360) and was subsequently omitted from the Peshitta, the official Bible in Syriac-speaking Christian lands in the fifth century.
In the West from the second century on the Apocalypse had won wide acceptance. In time the East began to reverse its earlier negative position. In the fourth century Athanasius in Alexandria endorsed it without hesitation. The Third Council of Carthage (397) listed the Apocalypse as canonical and appropriate for public reading in services. When the decrees of Laodicea and Carthage were ratified at the Third Council of Constantinople (680), the Apocalypse received formal acceptance as NT scripture in the eastern church. This favorable opinion was due in part to the first Greek commentaries on Revelation, which appeared about the sixth century.
Mounce, R. H. (1997). The Book of Revelation (pp. 23–24). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.