First line management tend to make less money then a top producing sales rep. They deal with HR issues, negotiations and hiring/firing of personnel.
Sales reps only have to worry about their #s and keeping clients happy for the most part.
Most comp plans for sales people are high leverage plans, where when a sales person hits his quota...they have accelerators that kick in. The manager usually needs most or all of the team to hit their numbers, for the managers accelerators to kick in.
So, again I ask you, as a sales person, is it in your best financial interest to be promoted to manager?