[wulf]

Putting the subject further away will increase the depth of field. It may be that those photographers want some of the quality of picture they get with quite a wide aperture but without a visible loss of sharpness on the subject, hence chosing a longer lens. If you are down at f/1.8 and close to, you can end up getting somebody's eyes in focus and the tip of their nose slightly blurred (an extreme example but you are certainly going to lose detail on what they are sitting on or standing in front of).

It may also be that they like other characteristics about the longer lens. One exercise to help is to take a series of pictures with both your lenses, making a note of how you adjusted the distance and seeing what effect it has.

Wulf