Why did this image was rejected?

For visual comparison, this is what you’re competing with in Stock inventory.

https://stock.adobe.com/search?k=ruby+gemstone 1.2 Million results

To be accepted, yours should be as good or better than what Stock is selling now.

Background elements aside, your gem has noticeable scratches and groove marks caused by unfavorable lighting.

There’s also a large blown out facet on the gem. 

Hello,

I think the foreground:

… the out of focus parts may be distracting.

I think the overall composition could be improved; you should try to show the stone off in its glory. It is a jem after all, and here it is nothing special—I think!

The type of lighting could be improved as well, and that is where AI may fail!

In addition, I believe the highlights on the stone need work. The white is completely without any details. 

Hi ​@Rodrigo Murasawa 

The file has noise grains and there is a blue color fringe around the white.

Best wishes

Jacquelin

Background is rather random. Square format is AI 101. A different aspect ratio might help with approving the background and composition. Some general cleanup need, but more must be done.