From 20 years of recruiting, two reasons.

1 - The high number is the only thing many candidates hear, which can lead to lost deals even when the offer is fair. Tell a candidate the range is 110 - 130K. Even if the candidate is "worth" 110K, an offer at 110 feels like a slight to him/her, as if he's left money on the table.

If there had been no range given in this case, the candidate might not have had the negative emotional response to the offer.

2 - There isn't a range because the company would be willing to accept a range of candidates, and a range of salary would not be useful. If you're willing to consider 2-7 years of experience, it's not all that useful to list 60-120K as a salary range.

Most of my clients never gave me a range.