If you read the transcript
I have, and they don't. Joan's return to transvestism was what brought her back before the trial judges:
And because Joan had put on the clothing of a man, that is to say a tunic, hood and doublet with other garments used by men, though she had recently abandoned this outfit at our order and taken the clothing of a woman, we questioned her: when, and for what reason, had she taken male clothing again?
And Joan replied that she had taken this male clothing just recently and set aside that of a woman. Asked why she had taken this male clothing, and who had induced her to wear it, she answered that she had taken it of her own free will, and that she preferred this male clothing to that of a woman.
She was then told that she had promised and sworn not to resume male clothing, but she replied that she never understood that she had made an oath not to resume this male clothing.
Asked once again for what reason she had taken it, she answered that she had done it because it was more lawful and convenient to wear male clothing when she was among men, than to wear the clothing of a woman. Item, she said that she had resumed it because what had been promised to her had not been kept, that is to say that she might go to mass and receive the body of Christ, and that she might be freed from her iron chains.
Asked if she had abjured before, and in particular sworn not to resume this male clothing, she replied that she would rather die than be in iron chains; but if she were allowed to go to mass, released from her chains and given a gracious prison, she would be good and do what the Church wanted.
Item, because we, her judges, had heard it said by some people that she had still not abandoned the illusions of her pretended revelations which she had previously renounced, we asked her if she had heard the voices of Sts Katherine and Margaret since Thursday [the day of the abjuration]. She answered yes.
Craig Taylor, Joan of Arc: La Pucelle, (Manchester, 2006), no. 55.
Now you've read a part of the official trial record, what is missing is a very important marginal note made against a particular phrase in this document:
Item, because we, her judges, had heard it said by some people that she had still not abandoned the illusions of her pretended revelations which she had previously renounced, we asked her if she had heard the voices of Sts Katherine and Margaret since Thursday [the day of the abjuration]. She answered yes.
[Marginal Note] Responsio mortifera
'The fatal reply'. This was what condemned Joan to death. Her transvestism was bad, but her heresy (her choice) to return to