The number one complaint of parents is their kids won't talk to them and the number one complaint of kids is their parents don't listen to them.
Madness string 96961
In any enterprise - business, military, academic, sports, etc. - leadership gets the behavior that they reward. Being a parent is a leadership position, and these parents have taught their other kids that acting like the middle sister is the behavior that they reward. They can't be surprised that their other kids have learned the lesson they've taught.