That's not what was being asked; what was being asked is "why wouldn't you want to persist some bits from a previous emission to a current one?" and the answer is "you do; it helps you in threat models where the attacker is somehow able to blast some hardware for a tiny time such that they can control an N bit-chunk of seed material, but not what came before or after." If you don't persist some bits between the calls, then this lets them determine entirely a few outputs of your RNG -- albeit scrambled by SHA3, but for some security expectations that's sufficient. On the other hand if you persist a seeding block between hash invocations, you block these attacks rather easily.