This is a point of confusion I still have with the simulation argument: Upon learning that we are in an ancestor simulation, should we be any less surprised? It would be odd for a future civilization to dedicate a large fraction of their computational resources towards simulating early 21st century humans instead of happy transhuman living in base reality; shouldn't we therefore be equally perplexed that we aren't transhumans?
I guess the question boils down to the choice of reference classes, so what makes the reference class "early 21st century humans" so special? Why not widen the reference class to include all conscious minds, or narrow it down to the exact quantum state of a brain?
Furthermore, if you're convinced by the simulation argument, why not believe that you're a Boltzmann brain instead using the same line of argument?