Aaron, statistical mechanics also depend on particle physics being time-reversible, meaning that two different microstates at time t will never evolve to the same microstate at time t+1. If this assumption is violated then entropy can decrease over time.

Is there some reason why time-reversibility has to be true?

If we can imagine a universe where entropy can be made to decrease, then living beings in it will certainly evolve to take advantage of this. Why shouldn't it be the case that human beings are especially good at this, and that is what they are being used for by the machines?