It is because I think this situation could have been avoided if

In this case, the sister/brother's mother was absent, and the sister's own hu*****and is also absent from his children's lives. The parent discarding his/her responsibility forced the siblings to take care of each other when they should not have to. If Chinese culture placed more value in commitment to children, spouses and the nuclear family (which is the predominant form of family in modern times), and had a more sound child welfare system, we should see such dilemma and cases of "indebtedness" decrease.