If you have been attending most of your life from a young age and dont make MS by say mid 20's, then your life tends to crowd out the possibility of enough service (WTS rules) as wives and kids take your time. The Elders then tend to see you as weak, and not recommendable. When I was young I guess I craved the position or title, but soon after I couldnt have allowed myself to be a part of the congregations politics, with all the MS' seeing what asignments they got and boasting about it. I'm certain I would hold back to not allow them to recommend me, as I dont know if I would have been able to say no, as others have said it seems a sin to say no at the time.
CS 101