because if this is such an 'easy' game just lay the 4. With the 4 at the vig its at its worth about -165 at best, so youre giving an extra 20-25 cents in vig. While there arent really sharps, there are certainly squares, and laying that much vig is as square as it gets.
although it is now down to -175, which is slightly more reasonable, but it still a dime too much. So in essence its like laying -120 when you should be laying -110 on a spread.
While getting the right side is the most important thing, over paying for it is a bad mistake, and if it ends up being the wrong side then it makes it even worse.