This is only when no other effects/processes are accounted for. If every participant keeps their current funds in an account with the same interest rate, then the distribution permanently skews so that there is no longer bobbing. The rich stay rich. See this more detailed simulation linked in another comment: https://joshworth.com/jpw/does-this-simulation-explain-why-l...

The paper this is based on [1] does a good job of spelling out:

The instantaneous distribution of money among the agents of a system should not be confused with the distribution of wealth. The latter also includes material wealth, which is not conserved, and thus may have a different (e.g. power-law) distribution.

The simulation might be a good model of how money distribution works, but it doesn't reflect how wealth distribution works. The simulation only works because money can neither be created nor distroyed (in the simulation, at least). Wealth can be so we shouldn't expect the simulation to predict its behavior.

[1]: https://physics.umd.edu/~yakovenk/papers/EPJB-17-723-2000.pd...

Does a fair system mean everyone is equal all the time, or everyone has the same chance of being poor or wealthy?