Because we see ourselves in the dysfunction.
Even experienced writers can fall into traps when writing families.
An eldest sibling who had to grow up too fast to care for parents or younger siblings.
That sentence carries ten, twenty, or thirty years of unspoken competition, parental neglect, sibling rivalry, and marital discord. In a family drama, the past is never truly past. It is a dormant volcano. Your job as a writer is to drill down into that history and release the pressure.