[Qayin]

It might be that working hour in Japan is very long, so women got to choose between career (plus independence) vs. family (and the man you mightn't be able to see him often because he come home late everynight) that might be the cause.

But I think the real problem is the same as everyone's idea. It's economic. With rising living cost, to conceive a baby might be too much to afford, especially in big city like Tokyo and Osaka. Life's very competitive. It's hard to make enough money to raise children nowaday. I think not only in Japan, but every big city in the world.