Yes, I agree that because of the intensity of the emotions that most parents have towards their children then it seems impossible for all parents to not have that exactly.
Yet, having grown up in a very abusive home then unfortunately I had firsthand experience when it wasn’t the case.
In fact, I simply had no idea that there were homes where parents loved their kids unconditionally.
I can’t speak for all causes, but one book on trauma went through the steps which occur when a parent with mental illness or an emotional disorder can’t connect with their children and how it can lead to abuse. I would have to reread it to remember the specific mechanisms involved.
I think that’s what happened in our household. My father was simply too scarred from his shitty upbringing that he never developed any sort of empathy or understanding that others were actually humans in their own right, and not just extensions oh him. He just wasn’t capable of love. For anyone or anything, including himself.