I think that sadly it is so universally accepted that men take less interest, less parental responsibility and frequently leave everything regarding home life and childcare to women that courts would have been very ready to believe in his ignorance.
Totally agree with you though.
There were two parents in that house.
Whether he lied or simply had a devastating lack of curiosity about his son’s health he is guilty of neglect at the very least.
Plus society loves a good “burn the witch” narrative so that would have some influence. Female wrong doing being less frequent than male draws more attention.
Clearly she is absolutely awful, selfish, cruel, abusive.
Personally, I don’t think that Munchausens by proxy is a mental illness. I think it is horrible, wicked behaviour by horrible, wicked people.
I had some of it in my own childhood, although nowhere near what happened to this poor little boy.