Help me understand why this photo was rejected?

It looks like you have great adventures. (I see no camera/info data in Photoshop). 

My first thought is that your photo seems over sharpened, or too much denoise, did you do any of both?

Are you using Lightroom or Photoshop?

I see a big opportunity for you selling you work from your hiking adventures, and I want to focus my advice to make this work for you. Here is the thing about landscapes… there’s too much of it, and yours is missing the appeal for a buyer.

first thing you need is choose your camera gear wisely, light and compact obviously. A tiny tripod a must.

Use your story of a hiker, add elements, back pack, boots, other gear, shoot yourself and partners using a timer and a tripod. Shoot a lot, vertical horizontal and bracket your exposers. If you're not an experienced photographer, go to YouTube U to get the basics, like always shooting in Raw, other settings and basic tutorials on Lightroom and Photoshop. On this particular image, I would darkened the sky a bit and warm the land.

One more thing, in bold letters:  SHOOT VIDEO 

I can't imagine visiting such amazing places and not shoot video also. DON’T worry if you don’t know how to edit right now. Like I said, you have an amazing opportunity to be successful selling stock… as long as you love shooting as you love hiking.

Feel free to write to me directly, I would enjoy guiding you more if you need and want to.

Best of luck!

Hello,

I think you need to add more contrast. The photo as it stands is a bit flat.

This after some quick adjustments, but not sure if you can see the differeence, but there is. 

I looked at the photo histogram in Lightroom. Your exposures are slightly off. You need to lower the highlights, raise the shadows and then adjust the blacks and whites until the histogram contains all of the tones.