edit: After checking a relevant Japan ministry of justice webpage [1], 5m yen is given as an indicator, which is why I suppose it is the value given by most lawyers.
[1]: http://www.moj.go.jp/nyuukokukanri/kouhou/nyukan_nyukan20.ht...
The money is still held by your company and you can own the stock, so it's not like you are "spending" it.
In addition to that, they already have lots of young people who can't find solid jobs. For the last 20-ish years they economy doesn't grow. Big companies usually keep their old employees for a really long time, but don't grow. Thus youth don't have positions to fill. Importing population wouldn't help much, most of their companies are export based.
I've been visiting Japan regularly for 20 years now. To a first approximation, nothing about the fundamentals above has changed.
The social changes are a much bigger challenge. If your family sees you as a bad mother for working while raising children then financial incentives and back to work schemes will only get you so far.
There's very little of euro/us style poor 3rd world kind of immigration. Even if one would get a visa, they'd have a really really hard time finding a job. Strip club bouncers is very limited market.
Japan just doesn't have a road for unskilled immigration (compared to the US with the green card lottery and all the illegal immigration, EU with all the refugee immigration). They had a program for nurse internship but apparently botched/sabotaged it.