Why does it imply a simulation? Perhaps it can be explained by an anthropic argument: Perhaps the kind of mechanics behind spacetime in which time evolution is computed in a stepwise manner depending on density are extraordinarily more likely because they somehow allow for much simpler mechanics (sets of laws with lower entropy are more likely to be the ones we find ourselves in, especially so if we assume that all non-physical sets of laws are realized as well, so that the impact of such a difference in entropy on the probabilties could be vast).