It does not fail. It's the expected outcome. Young people don't get "legal" independence until they get married. By "legal" independence I mean they don't have a personal register (koseki) until they have to leave the family register, which can basically only happen by marrying.

Besides, leaving at one's parents is not equal to be dependent, it is economically sound and young people who have entered the work force may live in the same place as their parents but few share much more than that.