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.
IE, I'm almost 30 and I've been living alone for 2 years only because I found a decent medium-pay stable job 3.5 years ago, and the apartment I live in is rented by a friend who asks very little money. All of my friends who are single like me live with their parents, and only a few of those who are engaged live with their partners.
I imagine different cultures are different, and things that are unattractive in America are attractive elsewhere, and vice versa.
That's extremely variable over time, and it's been very much in the rise in recent decades, IIRC.
Of course, it may be a matter where cultural attitudes toward behavior are much stickier than actual behavior.
Is living with someone else's parents more acceptable?