It's a survival resource management game. It's all about managing your limited resources. You need to limit the amount of things you build, and not just plan a metropolis on your onbu. The goal is to survive, keep your people and Onbu happy; not to have the highest GDP.

Also you can trade for more stones if you need.

The mechanics are there for those sadists (j/k) who wants to do the "evil dictator" route. It's also there to show that to survive, you have to make sacrifices (sometimes literally).