I think many Japanese are tough to accept marriage as a rite of passage in the course of the life. Social pressure to get married is very strong in Japan (or some other countries as well). I've been away from Japan more than 10 years since I turned 20; so, I don't subscribe to the cultural norm without any hesitation.
I am single and I just do not feel like getting married. Even though it would be nice to have a close significant other, I feel I would be shackled to the institution called marriage if I got married. My married male colleagues have to hand over their pay checks to their wives every month. I know I cannot do it as I am so used to spending what I have earned on whatever I feel like spending. Some estimates put a price tag of JPY 50 million for raising a kid for 22 years in Japan. I would rather keep that money in the mutual funds or stocks and use it for my early retirement. Some people want to get married and have children so that they don't feel lonely when they get old. By the time I would need to get in the home, my mental ability would be bad enough to recognize who is caring me.