For most of us, at least in theory, our families are supremely important. Regardless of bad behavior, family is still family. Blood runs thick.
When Jesus directed His mother to take His beloved disciple as her son, and his beloved disciple to take His mother as his mother, I think He was saying the same thing as He said in the parable of the sheep and the goats: we need to fully concern ourselves with the needs of others--to such an extent that as we care for others (or don't care for others), it is just as if we were doing it (or not doing it) for Him. And how we respond to Him is what is of the utmost importance.
For a powerful politician or business executive to give preference to a family member, it is considered unethical. Such behavior is called nepotism.
Natural human morality says we need to treat everybody equally well.
The Lord Jesus illustrates what this means by showing us that the woman in need is His mother.
For as much as you have done to the least of these my brothers, you did it to me. Matt 25:40