Why does it seem likely that we're in an ancestor simulation rather than being in a simulation of some other sort? We could be in a game, or a non-historical educational tool, or a big hobby project. Or, of course, in something which doesn't correspond to any of our motivations.

We create a huge number of simulations in fiction and history and gaming. Some of them are more or less accurate, many of them aren't. Our simulations do tend to resemble us, or at least our models of what's interesting about us, but I'd assume that a more advanced civilization would have a wider range of invention.