I have explained why.
I have cited them.
I don't. But if I did, what is it to you?
Another way of looking at it is 1 billion Catholics worldwide are obligated to believe in Purgatory.
Oh?
-- Clement of Alexandria
The believer through discipline divests himself of his passions and passes to the mansion which is better than the former one, passes to the greatest torment, taking with him the characteristic of repentance for the faults he may have committed after baptism. He is tortured then still more, not yet attaining what he sees others have acquired. The greatest torments are assigned to the believer, for God's righteousness is good, and His goodness righteous, and though these punishments cease in the course of the expiation and purification of each one, "yet" etc. (Patres Groeci. IX, col. 332 [A.D. 150-215]).
-- Origen
If a man departs this life with lighter faults, he is condemned to fire which burns away the lighter materials, and prepares the soul for the kingdom of God, where nothing defiled may enter. For if on the foundation of Christ you have built not only gold and silver and precious stones (I Cor., 3); but also wood and hay and stubble, what do you expect when the soul shall be separated from the body? Would you enter into heaven with your wood and hay and stubble and thus defile the kingdom of God; or on account of these hindrances would you remain without and receive no reward for your gold and silver and precious stones? Neither is this just. It remains then that you be committed to the fire which will burn the light materials; for our God to those who can comprehend heavenly things is called a cleansing fire. But this fire consumes not the creature, but what the creature has himself built, wood, and hay and stubble. It is manifest that the fire destroys the wood of our transgressions and then returns to us the reward of our great works. (Patres Groeci. XIII, col. 445, 448 [A.D. 185-232]).
"As John stood near the Jordan among those who came to be baptized, accepting those who confessed their vices and their sins and rejecting the rest ... so will the Lord Jesus Christ stand in a river of fire next to a flaming sword and Baptize all those who should go to Paradise after they die, but who lack purgation... But those who do not bear the mark of the first Baptism will not be baptized in the bath of fire. One must first be Baptized in water and Spirit so that, when the river of fire is reached, the marks of the baths of water and Spirit will remain as signs that one is worthy of receiving the Baptism of fire in Jesus Christ." (Origen, Commentary on Luke, 24th Homily, before 253 A.D)
-- Tertullian
"This place, the Bosom of Abraham, though not in Heaven, and yet above hell, offers the souls of the righteous an interim refreshment until the end of all things brings about the general resurrection and the final reward." (Tertullian, Against Marcion, 4:34, before 220 A.D.)
-- Cyprian
It is one thing to stand for pardon, another thing to attain to glory; it is one thing, when cast into prison, not to go out thence until one has paid the uttermost farthing; another thing at once to receive the wages of faith and courage. It is one thing, tortured by long suffering for sins, to be cleansed and long purged by fire; another to have purged all sins by suffering. It is one thing, in fine, to be in suspense till the sentence of God at the Day of judgment; another to be at once crowned by the Lord (Letters 51[55]:20 [A.D. 253]).