Is it because Ozai is an evil jackass that he is excused? Where Ursa is a loving mother that would have done anything for Zuko (and probably Azula) that makes her not? Or is it the fact that she is a mother that people don’t excuse it? I believe she loved both of her children, but with Ozai’s paying so much attention and love to Azula why is it not okay that Ursa does the same thing for Zuko? Azula might have needed to be shown the love of a mother, but I believe Ursa really truly did love her. But Zuko needed to be shown the love of a father, and it was clear that Ozai was basically only ashamed and disappointed in him. Ozai told him he was lucky to be born. He banished him. Ursa would have never done that (Even if she had the power). Zuko had to grow up feeling that he had to restore his honor and knowing his father basically didn’t love him, and had no idea where his mother was. Azula might not have had a mother either, but she had a father that she knew loved her. Azula and Zuko both had it really hard with one parent favoring the other, not just Azula.
(I am not by any means saying that no one is criticizes Ozai, but in the past few days the only cirtizim falls on Ursa and it just isn’t fair)