Everything comes down to motivation. When it's you and three other people, you can figure out a system. It's very easy to enforce the system because you all know each other. Not working well lets them down and lets them beat you down.
When it's you and a village, it's still relatively easy to enforce things because you have families and relationships. There's some inefficiency and some corruption from individuals but you can still try and monitor everything.
When it's you and a hundred million people, you could never even meet everyone let alone know them. So you need a thousand steps between. And every step and every system can have corruption and inefficiency. Unless you have some sort of central mandate like religion, it's very hard to motivate people because everyone is so separated. Even if you do, you still get corruption like in china.
When it's you and a village, it's still relatively easy to enforce things because you have families and relationships. There's some inefficiency and some corruption from individuals but you can still try and monitor everything.
When it's you and a hundred million people, you could never even meet everyone let alone know them. So you need a thousand steps between. And every step and every system can have corruption and inefficiency. Unless you have some sort of central mandate like religion, it's very hard to motivate people because everyone is so separated. Even if you do, you still get corruption like in china.