I was wondering why the father’s namaz and fasting is wajib to make up and the moms is not. Even though the mother probably missed majority of her faces due to pregnancy. Whereas an average healthy male has no valid reason to miss fasts. It’s hard for me to wrap my head around this as Islam has such a high value for women and specifically mothers. If you could kindly explain or point me to some books so that I can understand this better, I would appreciate it.

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When something is wajib, you have to do it, otherwise you are punished, while when you do the recommended thing, your grade is much higher. Please note that Allah SWT praised the people who are praying Tahajjud more than the people who are just praying the 5 prayers.
Hence, when the son makes up mother's prayers, he is rewarded more by Allah SWT. On the other hand, making up father's prayers and fasts are the duty of the oldest son only, because he inherits certain items of father belongings, above his share of inheritance.