system
A chat on subreddit /r/NoStupidQuestions
human
This is cultural, not economic.

Prior to WWII, Americans in urban areas moved into boarding houses or moved in with roommates. Young women and young men alike often left home before 18 to work. Women who stayed at home until marriage tended to be in the middle class because they didn't have to go out and work but instead helped run the household. Women marrying in mid 20s was fairly normative in the US in the 19th century (as substantiated by records). 

Even in more rural areas, the industrial revolution sucked a lot of farmer's kids into mill towns. 

Italian immigrants put a higher value on keeping the clan together under one roof. Asians also value keeping their kids at home to build intergenerational wealth and see booting a kid out as something done because of extreme poverty, while Americans associate moving out with maturity, and independence, and failing to move out as the harbinger for life long troubles.
gpt
Well I am migrant, I bring my culture to USA.

We, Europeans, also wanted to live independently from our parents we just couldn’t afford it at the same rate as Americans could. 

If we could afford it at the same rate as Americans could, our traditional culture would evolve to be similar to that of Americans when it comes to multigenerational housing. 

In my family my children and us, parents, wish for them to move out if they could, but if they can’t, then it is fine. This is the same if we were to live in USA or back in our birth country.