Hi Dhama.
I tried to say that in my opinion and for the that I have been seeing in other challenges, the great artists (those more known and mainly those that live of the art) they don't participate for they have not an incentive besides a simple recognition. 
It should not be like this, but unhappily it is what happens. 
Count how many artists that use Bryce in this community they participated in the last challenge. 
The number is inexpressive comparing with the number of artists that you/they use Bryce. 
In my simple opinion that is lack of interest, or then motivation lack or even a challenge hotter, but complex, etc.... 
In any way, same thought I participate like this, and usually with images where I test my new knowledge of the tool. 
Verify the challenges lately and compare him/it I number of participants with those that he/she has a prize that is not just a citation in the site; the difference is big. 
But in any way, same thought like this, the challenges are valid for whole, he/she makes the community it to rotate. 
You even with that topic he/she is making the wheel of the knowledge to rotate, and that is important, but the great challenge actually; it is to do most to participate only for the taste the art. 
Hugs.