Most people here have scored based on the fact that this is a "Rock, Paper, or Scissor" challenge, meaning one of those three should be the focus of the shot. The key word being focus.
I, on the other hand, read into this challenge in a more literal way. i.e. 'your photo should contain one or more of the three items'. The instructions did not mention focus. As a result, one of those 18 7's votes were mine. :-)
While your photo does contain a rock thats not the focus of the photo... so just repeating that over differently - while it does meet the challenge, the challenge really isnt the focus of your photo.
That being said, ignoring your final score and looking at the vote distribution more than 1/3 of the people gave you a 5. meaning there isnt really anything wrong with your photo but it doesnt really have anything special about it in relation to the challenge. The next marks are 4s,6s,3s and 7s. And this just accounts for different peoples average vote given + whether they liked it a little or disliked it a little. A few people really liked it and a few people really disliked it... so thats how you ended up at a 4.8
I never even made into this challenge submission or vote-wise, and
here is my take on it (for what it's worth):
What is the first thing that gets my attention is this shot?
The young lady (you?) posed nicely here. The black & white was a good choice for the post-processing as it generates a mood and takes away the distractions that color can bring into a shot. Perhaps a little more smile (I'm such a sucker for an attractive lady/model with a nice smile) would warm the shot, maybe not. There's a nice contrast between the light pants & dark rocks and the dark hair/shirt & the light sky.
At no point have I mentioned the rocks. They are a nice setting for this portrait, but are not the focal point of the image. Rocks, Paper, Scissors - any of which "should" have been the strong point to a voter, not a supplemental part of the shot. Granted, the rocks are numerous and well represented, but I can only suspect the voting majority never saw past her.
On a side note, this is a great picture! Your post-processing here was just right. I would have been proud to produce a shot like this.