But publishers sometimes get that wrong, don't they? Predicting the success of a given novel? We've seen that before, and honestly, it would worry me (though it would be very flattering in some respects) to have a really high advance offered for my work.
Odds are good that I'll likely end up going with a smaller press and never write a blockbuster type of novel as a result, and that means finding an agent who is on the same page I am. Or submitting to publishers directly where I can. (Shoot, odds are excellent that I wouldn't write a book like that anyway, who am I kidding, lol)
A bird in hand might be worth two in the bush for some, but not all.

And there are some smaller presses putting out really excellent books, publishers I'd be honored to by published by, but they don't --by and large-- offer enormous advances. Algonquin comes to mind immediately. Doesn't mean that they
won't, just that they normally
don't.
Maybe I've got the wrong end of the stick here, I don't know. But frankly, I'd be thrilled to get a book contract in the first place, so....