The parent-child relationship is the root of self-cultivation and political order. The child learns how to act in society and be respectful to others within the family unit. Filial piety is thus a core moral concept.
Kwong-loi Shun “Xiao (Filial Piety)” Encyclopedia of Chinese Philosophy 2003
Though evolution pushes us toward kin selection (assuring survival of blood related humans, first), there is no moral requirement to help anyone, including one's parents. It's particularly understandable that one would not help another person who has treated them badly, harmed them, neglected them.
Morality is not objective, as such who are you to declare it a moral obligation? It could be argued to be perhaps ethically preferable, but to say I am obliged to treat my parents well is false.What about a child that is, say raped or beaten by his parents? Why should he treat his parents well?