My 2 bits here-

A big part of the challenges is to provide "amateur" or hobby map makers with some motivation to complete a map within a fixed time. It helps to develop focus and is a good prep to build a "virtual portfolio" outside what they might create just mapping for themselves.

Anyone who is routinely making maps on a commission basis are free to participate, but most likely won't have the time, or have other priorities/goals in mind (as nicely stated by GP).

This is really the reason we chose the term "challenge" rather than "contest" in the first place... it is not intended to be a "one winner, the rest losers" contest but a challenge to every person to better themselves, given a set of constraints!

-Rob A>