[poster1]

Another possible explaination is that there is much less inequality in Japan than in the UK. (observe the relevant Gini co-efficients)

By having less economic inequality means a greater economic mobility within a country.

Hence it is relatively easier for a Japanese girl to pursue a reasonably wealthy lifestyle than a similar economic background girl in US or the UK - assuming equal in relevant skills in job market.

So by getting pregnant, a Japanese girl has much more to lose than a similar counterpart in UK or the US. This is a highly likely explaination since it is based on empirics.