I think the best argument for why we are not in a simulation is this: Given that civilization has advanced to the point where we can create a simulated environment so perfect that it would fool us into believing it is reality.
Why wouldn't we have picked a better time period to recreate?
What kind of twisted mind would choose to relive this time period? What, was the Great Depression already checked out at the SIM library? Dark Ages not returned yet because "Ya just can't get enough of the Bubonic Plague"?
How about "because someone is trying to prove a point to somebody else" that requires these initial conditions?