I think because there are so many parents here, it hurts them to think that their children might not love them if they don't treat them right. so it's easier to make out the child is the unreasonable one, and a parent can't be at fault.
Bang on, I think. It's much easier to accept that your child is just a nasty piece of work, or inherently insane beyond redemption, than that you were an appalling parent and caused the damage. If you had an abusive parent yourself, it can be unbearable to think that you became the thing you hated most.
That's one reason why there's usually a golden child alongside the scapegoat. If you elevate the child who doesn't display the damage you did in such a revealing way (in my experience they are usually damaged too but they show it differently) then you can use them as "proof" that you're not to blame because this child turned out great, doesn't blame you, etc etc. And then you can weaponise that dynamic among the kids to deflect everything from yourself, and punish the scapegoat for not falling in line. I don't think many abusers do this consciously, but they definitely do it.
It is very interesting how many kids, faced with a golden child/scapegoat dynamic, do indeed blame each other and not their parents. I'm not religious any longer but I remember as a teenager, looking at the story of Joseph and thinking, "Don't blame him, brothers, blame your arsehole dad!"
But I lost any need for my father's approval at a very young age.