If natural discharges necessitate ablution for every prayer, then what is the difference between them and the blood of Istihada, which we have considered a sickness and given the same ruling? And does this cause hardship for women?

Prayer requires purification from ritual impurity. The discharge of fluids from a woman is an impurity that necessitates purification for prayer. If her impurity is continuous, then she must perform ablution for every prayer, because she is treated like a woman with prolonged vaginal bleeding (mustahadah) in the continuity of the impurity.