I think mostly it can be due to how you are coping with the pg, some cope better than others, some are frightened of being overdue or being induced. For me it was starting pre-labour at 37wks getting to 3 cm dialted, contractions stopped and then was sent home, had a bad pg and felt awful and contractions didnt start again for another 5weeks. DS was on the larger end of the scale (over 4 and a 1/2kg) and next time I will do everything to try and bring on or keep those contractions coming. As spring angel said some have other circumstances where they really want to see there bubbies born happy healthy and safe as fast as they can. (not to soon though)
On another note the RLT has the benefit of uterine toning so helps your uterus to return to its normal size sooner after birth and can assist with breastmilk production. So if nothing else I think that is a benefit.