The fact that Mary was MARRIED to Joseph is prima facie evidence of the fact that she did not remain a virgin. A marriage (by catholic tradition) is not official unless and until it is consummated.
Further the scripture clearly implies that her virginity was not perpetual;
And knew her not till she had brought forth her firstborn son: and he called his name JESUS. (Matthew 1:25 KJV)
So the chances are that there was no teaching on the perpetual virginity of Mary is simply because the scriptures state that she wasn't. It wasn't an issue because it wasn't an issue.
It think we can assume that Mary was always chaste. We cannot logically or scripturally assume that she was always a virgin.
Being married doesn't require one must consummate the marriage, 2000 years ago. You are being anachronistic.
I would suggest you read the following link, which will answer your questions regarding marriage and celibacy in Jewish tradition:
http://www.cin.org/users/james/files/talmud.htm
Among some of the items in this link is the following:
"We also have to take into consideration that when Mary was told by the archangel Gabriel "Behold, you shall conceive in your womb, and bring forth a Son, and you shall call His name Jesus" (Lk 1:31), he also added that this was to come about because "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the Holy one to be born shall be called the Son of God" (Lk 1:35).
By stating it in those terms the archangel declared to Mary that God would enter into a marital relationship with her, causing her to conceive His Son in her womb, For "to lay one's power (reshuth) over a woman" (Targum to Dt 21:4) was a euphemism for "to have a marital relationship with her."
Likewise "to overshadow" (Lk 1:35) by spreading the "wing" or "cloak" over a woman was another euphemism for marital relations. Thus, the rabbis commented (Midrash Genesis Rabbah 39.7; Midrash Ruth Rabbah 3.9) that Ruth was chaste in her wording when she asked Boaz to have marital relations with her by saying to him "I am Ruth you handmaid, spread therefore your cloak ( literally, "wing": kanaph) over your handmaid for you are my next-of-kin" (Ruth 3:9).
Tallith, another Aramaic-Hebrew word for cloak, is derived from tellal = shadow. Thus, "to spread one's cloak (tallith) over a woman" means to cohabit with her (Kiddushin 18b, see also Mekhilta on Exodus 21:8). Did not the Lord say to His bride Israel: "I am married to you" (Jr 3:14) and "your Maker is your husband"? (Is 54-5:5; Jr 31:32)? And what is more intimate than what the Lord said to His bride: "You developed, you grew, you came to full womanhood; your breasts became firm and your hair grew... you were naked... and I saw that you were now old enough for love so I spread my cloak over you... I gave you My oath, I entered into a covenant with you and you became Mine, says the Lord God" (Ezk 16:7, 8).
Mary prohibited to Joseph
Having been enlightened by an angel in a dream regarding her pregnancy, and perhaps further by Mary concerning the words of the archangel Gabriel to her at the Annunciation, Joseph knew that God had conducted himself as a husband in regard to Mary. She was now prohibited to him for all time, and for the sake of the Child and Mary he could only live with her in an absolutely chaste relationship."
You certainly are not the first person to question such a teaching of the Church. The fact remains that this was all carefully thought out by the Church many many years ago when they first pored over the Scriptures and the meaning behind the surface of Scriptures.
Regards