You're now basically saying "because magic!". Sure the outer universe could be based on something else but the thought experiment is that we'd be doing this in

You're now basically saying "because magic!". Sure the outer universe could be based on something else but the thought experiment is that we'd be doing this in our universe. It doesn't require some other universe with magic unknown properties, it requires first that we can do this in our universe to a sufficient level that NPCs in simulations in our universe can't easily see the issues.