In your example you start with 4 players each having $100, but IRL there are many more players with many more dollars who can and will join this game and 4 original players will eventually willingly or unwillingly exploit them.

It's like Israeli Kibbutzim[1] had a members-only Communist-like system, by exploiting outside employees and living on government subsidies.

Most kibbutzim are not self-sufficient and have to employ non-kibbutz members as farm workers (or later factory workers).

[1] https://en.wikipedia.org/wiki/Kibbutz

market is a closed system.