What is the evidence as to why a menstruating woman needs to make up for her missed fasts but not for her prayers?

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Mu’adha al-‘Adawiya said that when she asked ‘A’isha (ra) why one who has been menstruating must make up for her fast but not for her prayer, she replied, “That happened to us, and we were ordered to make up for the fast, but were not ordered to make up for the prayer.” [Muslim]