Upvote:6
I think that a distinction needs to be drawn between authentic in the sense that the works were historically authentic (i.e. indeed written by the Dionysius of Acts) and authentic in the sense that they correctly reflect Apostolic teaching.
Eastern Christian theology is not based so much on the former as the latter. The Pseudo-Dionysian corpus was not so much accepted because the latter Fathers thought it was written by Dionysius (which many seem to have believed), but rather because of the clarity with which it expressed certain truths which they held.
To perhaps further shock, Pseudo-Dionysius continues to remain an important part of the written tradition of the Eastern Orthodox Church to this day, despite full awareness of the issues with its historical authenticity. The entry on Dionysius in the text of one prominent Russian Orthodox theologian reads, for example:
St. DIONYSIUS the Areopagite --- A.D. 96
A disciple of the Apostle Paul (Acts 17: 34), first Bishop of Athens, martyred in Paris; commemorated October 3. To him have been attributed a number of works (Mystical Theology, The Divine Names, The Heavenly Hierarchy, The Ecclesiastical Hierarchy) which formulated the basic Orthodox teaching on these subjects and inspired later Orthodox theologians from the time of St. Maximus the Confessor (7th century). Because his works seem to have been unknown in the first Christian centuries, and in a style and content seem to be later in date, it is generally accepted that in their present form they are of the 5th century. Modern scholars therefore call the author “Pseudo-Dionysius,” but in the Orthodox world, where the concept of “authorship” is not so restricted, there is no difficulty in seeing these works as in the tradition of St. Dionysius — and through him, of St. Paul.1
This sentiment is echoed in one of the most important Orthodox Christian theological works of the 20th century - based largely on the writings of Pseudo-Dionysius - Vladimir Lossky's The Mystical Theology of the Eastern Church:
Modern critics, so far from agreeing as to the identity of the ‘Pseudo Dionysius’ and as to the date of the composition of his works, wander amidst the most diverse hypotheses. The way in which the critical researches waver between dates as far apart as the third and sixth centuries shows how small a measure of agreement has as yet been reached in regard to the origins of this mysterious work. But whatever the results of all this research may be, they can in no way diminish the theological value of the Areopagitica. From this point of view it matters little who their author was. What is important is the Church’s judgement on the contents of the work and the use which she has made of it. Does not the author of the Epistle to the Hebrews say in quoting a psalm of David: ‘But one in a certain place testified …’2? thus showing to what extent the question of authorship is of secondary importance in the case of a text inspired by the Holy Spirit. What is true of Holy Scripture is also true of the theological tradition of the Church.
So the answer I would give to your question, "Why were Pseudo-Dionysius's works accepted as authentic for so long?" is that historical accuracy was not as important issue as might be imagined in the eastern Church - with a footnote that the works are still accepted as being theologically authentic, even if their historical origin is in question.
1 Michael Pomazanski, Orthodox Dogmatic Theology (3rd ed.), p.382
2 Hebrews 2:6