Why are there so few women in a position to lead political parties in Japan?

History, culture, resistance to change. It will turn up better since it is impossible to remain like this, but it may take still another generation or two.

Blame it on the aging population...

I think we all know the reasons, but I just don't care anymore. Not my country, so it's not my loss. Just look around Asia - India, Bangladesh, Pakistan, Indonesia, Hong Kong, Taiwan, South Korea, the Philippines. What do they all have in common? To make things worse, North Korea might join this group if Kim Jung Un kicks the bucket! And no, I'm not talking about English proficiency levels!

Perhaps fewer women are interested.

maybe because many of them know that political parties are a joke in Japan, and its just a waste of time.

This probably goes all the way down to grass roots.

I do feel that more women proactively voting for female candidates would help. People may moan about ojisans, but they keep re-electing them.

There are so many areas where we all need to suspend disbelief.

Not just a Japanese issue.