A Very Good Question! And the answer is nothing less than the fact that my substantiated interpretation of Scripture as regards RC Purgatory is far and away superior to that of Saint Gregory, who I do not see even text-proofing RC Purgatory, but argues for fire purifying man inn the context of the Resurrection, with this being being “the reconstitution of our nature in its original form" "with the casting off of that tunic, fling from us all the belongings that were round us of that skin of a brute; and such accretions are sexual intercourse, conception..."
Which one could try to say 1 Cor. 3 refers to, but which event incontrovertibly takes place at the second coming and the resurrection of believers, and not indeterminate purifying commencing at death, with punishments to atone for sins and make one perfect in character.
And again, it is absurd that the doctrine as Purgatory would not be clearly taught when the second coming and the believers transformation, and the judgment seat of Christ is clearly taught.
Thus the recourse to Tradition, yet even then you have competing contradictory claims as to what it teaches. Thus you have EOs who assert,
The Orthodox Church opposes the Roman doctrines of universal papal jurisdiction, papal infallibility, purgatory, and the Immaculate Conception precisely because they are untraditional." - Orthodox apologist and author Clark Carlton: THE WAY: What Every Protestant Should Know About the Orthodox Church, 1997, p 135.
►Both purgatory and indulgences are inter-corrolated theories, unwitnessed in the Bible or in the Ancient Church.. — http://www.goarch.org/ourfaith/ourfaith7076
►The Orthodox Church does not believe in purgatory (a place of purging), that is, the inter-mediate state after death in which the souls of the saved (those who have not received temporal punishment for their sins) are purified of all taint preparatory to entering into Heaven, where every soul is perfect and fit to see God.
Also, the Orthodox Church does not believe in indulgences as remissions from purgatoral punishment. Both purgatory and indulgences are inter-corrolated theories, unwitnessed in the Bible or in the Ancient Church, and when they were enforced and applied they brought about evil practices at the expense of the prevailing Truths of the Church. If Almighty God in His merciful loving-kindness changes the dreadful situation of the sinner, it is unknown to the Church of Christ. The Church lived for fifteen hundred years without such a theory. — http://www.goarch.org/ourfaith/ourfaith7076
Roman Catholicism, unable to show a continuity of faith and in order to justify new doctrine, erected in the last century, a theory of "doctrinal development." Following the philosophical spirit of the time (and the lead of Cardinal Henry Newman), Roman Catholic theologians began to define and teach the idea that Christ only gave us an "original deposit" of faith, a "seed," which grew and matured through the centuries....
On this basis, theories such as the dogmas of "papal infallibility" and "the immaculate conception" of the Virgin Mary (about which we will say more) are justifiably presented to the Faithful as necessary to their salvation. - http://www.ocf.org/OrthodoxPage/reading/ortho_cath.html
More .
By no means, but because distinctive Catholic teachings are not manifest in the only wholly inspired substantive authoritative record of what the NT church believed (including how they understood the OT and gospels), which is Scripture, especially Acts thru Revelation. .