I mean, think about it. My grandmother was a piece of shit, which caused my mother to be a piece of shit.
So this probably also happen in affluent families. One of those families is gonna be the ruling dynasty. So in the beginning somebody send an army to conquer lands. Then was really strict (aka: abusive) towards his children in order to find the “perfect” hier to the kingdom/empire. Because of the abuse, the heir grows up to be a tyrant. This chain reaction lasted for centuries, which is why our world is just tyranny after tyranny.
Obviously this is not to say it absolves the tyrants of their wrongdoings, but its the explanation.
You’re jumping over points here a lot… Yes children who were raised to be a piece of shit will probably raise their children to be a piece of shit, but it doesn’t necessarily mean they’ll be the ruling family.
There’s examples of hereditary rule where the ruler is a great and largely fair leader, such as Pedro II and Elizabeth I, as well as the opposite, such as Kim Jong Un and Ferdinand VII, as well as great and tyrannical elected leaders, and great and tyrannical leaders who came to power militarily.