I really think it's just a combination of the experts sticking with their horses and hoping they end up looking prescient as well as the simple fact that there's no way they can do all the homework it takes to keep current on every player. At least during the season, as Kyle mentioned. With some (cough Keith Law cough), I think there is a lot of ego involved. Switching up now would entail conceding their initial assessments were off, which would be unacceptable. They'll ride their horses all the way into oblivion like Slim Pickens on his nuke, if need be. And if it comes to that, they will only have been wrong because something "unforeseeable" happened. Bingo.