Because UF still had games left to play and the voters took a "wait-and-see" attitude. They probably didn't expect UF to beat Arkansas. I thought UF did an excellent job yesterday, and they dominated Arkansas enough. They shut down their running game, and scored 31 offensive points (the first SEC opponent they've managed to get 30+ points against).
If "they" didn't expect Florida to beat Arkansas why was Fla rated #4 and Arkansas rated #8?