[dragonwriter]

> I don't understand why parents would let their adult children live with them for years on end.

Extended families living together had been very common across cultures and times; as has people living with parents, if not permanently, until marriage, however late that may or may not happen.

Unconditional ejection at the entrance to legal adulthood is, arguably the odd thing.

> Isn't 18 years of imprisonment bad enough?

Not every family situation feels equivalent to imprisonment for the child or enslavement for the parent.