We live so far from the events that we often look at things in a vacuum.
Perhaps you missed how Clement of Alexandria refuted the PoJ's notion of Christ's birth?
Clement of Alexandria, c175
But, as appears, many even down to our own time regard Mary, on account of the birth of her child, as having been in the puerperal state, although she was not. For some say that, after she brought forth, she was found, when examined, to be a virgin.3666
3666 [A reference to the sickening and profane history of an apocryphal book, hereafter to be noted. But this language is most noteworthy as an absolute refutation of modern Mariolatry.]
Now such to us are the Scriptures of the Lord, which gave birth to the truth and continue virgin,
Clement was refuting the type of birth (not normal) shown in the PoJ that left Mary in the pueperal state (full of afterbirth). Though she was not (because she did in fact give birth normally). IOW, her 'virginity' was left intact is what PoJ says. (Then this is picked up in the gnostic east gate is shut. Not south gate, but east gate with the implication Christ was born from her side, leaving the hymen intact). No normal birth, but rather, a light recedes and a YOUNG CHILD APPEARS (not a baby). It takes the breast says the PoJ, rather than as expected, the mother lifts him to her. Clement like myself and others rejects that spurious, gnostic nonsense.
A short 20 years later, Tertullian will battle against the same gnostic idea proposed by the PoJ.
This man having first fallen from the principles of Marcion into (intercourse with) a woman, in the flesh, and afterwards shipwrecked himself, in the spirit, on the virgin Philumene,70247024 See Tertullian, de Præscr. Hæret. c. xxx. proceeded from that time70257025 Ab eo: or, from that event of the carnal contact. A good reading, found in most of the old books, is ab ea, that is, Philumene. to preach that the body of Christ was of solid flesh, but without having been born.
http://www.ccel.org/ccel/schaff/anf03.v.vii.vi.html
So, while we may try to read PoJ after 2000 years, they knew what was at stake.