Japanese 18-30 year olds are also in a lot less debt. It's part of the Japanese culture to live with your parents until marriage and it has nothing to do with independence. There are also plenty of young people who move into expensive tiny single bedroom apartments in Tokyo for work purposes. But who would want to do that when you can live in a private wing of your parents house for free? Most young people spend their social time outside of their houses anyway (house parties in the west vs karaoke parties in Japan). It just ends up being a place to eat and sleep.