There's also a distinction between rules that were created by the legislature, possibly motivated by emotion as you describe, and rules resulting from interpret

There's also a distinction between rules that were created by the legislature, possibly motivated by emotion as you describe, and rules resulting from interpretations by courts. While the former has no limits on their reasoning process, the latter is supposed to stick to the intentions of the law, which would preclude emotional decisions. Presumably the rule is there to subsidize child-rearing. When the child is gone (kidnapping, death, ascention to heaven, etc), the law would logically not apply any more, so there will be details about where the cuttoff falls. If people wanted want to give cash to unfortunate parents, judges interpreting the laws should tell you to pass another law for it.