I thought the same thing when looking at my pool the other day. I found it very realistic that the water was still after no movement in it after a period of time.
My point is that we don’t know the forces that the simulation is intending to model. There may be water flowing in/out along the z-axis, for example. Or there could be wind. Assuming that the author intended to simulate the same conditions in your pool, and then criticising them for not modelling it accurately enough, makes no sense to me.
