As P pointed out elsewhere, that's usually because predicting outside of the top 10-15 is difficult. At best, you're just looking at positional fit or priorities. Compare that to, say Arizona in the top 5. Unless they trade out, they're likely to pick just one out of two or three guys only.
For instance, nearly every mock has us taking WR, CB, or IOL. I may have seen one or two with us taking EDGE too.