Can't find sources for my guesses. This is the closest, showing the ratio of women to men in rural areas went from 99.8 in 1990 to 99.0 in 2000. My guesses are:
- in the old days, women were more conservative in rural areas, men could migrate to urban areas for jobs, both manufacturing and others.
- smart rural women could find jobs as teachers.
- smart rural men went to college and ended up in jobs in urban and suburban areas.
- the sex ratio was heavier female (despite the "norwegian bachelor farmers")
- in the modern world more women go to college and end up in jobs in urban and suburban areas.
- women are now more into social issues and tending to be liberal.