Because kids are super sensitive and will always follow the lead of their parents and people around them.
Especially if there aren’t any direct consequences to their actions.
It’s always the youngest sibling because they’re still young enough to backpedal from the conditioning and also have the unique perspective of seeing from a slightly different perspective.
It’s not a perfect explanation but I think it’s probably the premise most writers use.

It was always the one who bullies fl or the most rowdy one who apologize first to fl in this going back to the past after being killed or cause of death is family stories... And I wonder why...