Someone has to be the favourite.
We're inarguably the biggest club in the division based on recent history. We were relegated despite (on paper) being more than strong enough to survive the Championship (and barring a points deduction, we would have done).
Yes, we've had quite a bit of upheaval over the summer, but we've got a manager who has had success with a similar club to ourselves, we've recruited strongly for the division (again, on paper), we've got more depth than most the division in most positions. Most of the younger players we've got would've been expected to at least be at league 1/2 clubs on loan last year so this is a natural level for them now, and some have a much higher ceiling (Alves/Braybrooke). The older players we've brought in like Cullen/Chaplin/Burns are all experienced at this/a higher level.
We have issues and glaring gaps in the squad, but every side in this league does otherwise they wouldnt be here. Will we live up to that expectation? Possibly not. But its not hard to see why we're up there as favourites. Not to mention that the betting odds are self-driven so the more money thats put behind us, the more it reinforces us as favourites...