The obvious guess is that theists are more comfortable imagining their decisions to be, at least in principle, completely predictable and not “fight the hypothetical”. Perhaps atheists are more likely to think they can trick omega because they are not familiar and comfortable with the idea of a magic mind reader so they don’t tend to properly integrate the stipulation that omega is always right.
The obvious guess is that theists are more comfortable imagining their decisions to be, at least in principle, completely predictable and not “fight the hypothetical”. Perhaps atheists are more likely to think they can trick omega because they are not familiar and comfortable with the idea of a magic mind reader so they don’t tend to properly integrate the stipulation that omega is always right.