that's by choice, if they wanted they can get isolated and be self sufficient with some minor compromises/inconveniences
[1] https://www.merlofarminggroup.com/agri-view-japan%E2%80%99s-...
same with food, it's just not worth for them right now, quite irelevant comparing status quo with situation where you want to be isolated not part of globalized system, just because now they import 60% food doesn't mean they need to import 60% of food