A smaller population allows you to devote more resources per capita while reducing the resource consumption of the population as a whole. Apart from the obvious

A smaller population allows you to devote more resources per capita while reducing the resource consumption of the population as a whole. Apart from the obvious appeal of enjoying at least comparatively luxurious allocation of public resources, this can have real benefits for a modern knowledge economy; having more educational resources to devote per-child can give your country a leg-up on those that have to use their funding on a much larger, ever-growing student body. Put another way, which problem would you rather have: desperately trying to keep 2000 inner city youth from dropping out of a school that is halfheartedly going through the "everyone should go to college" motions and not really teaching them anything relevant or helpful to their life track so that the majority can graduate into minimum wage service jobs at best or end up on welfare or in a gang at worst, or teaching 20 everything you know about web development or some other marketable trade that can lift them out of the vicious cycle? I don't really know anything about Japan's education system beyond serafuku, but this is the way I see the world moving in the somewhat near future as manual labor and service jobs continue to fall to automation.