Digital painting rejected—would love to know what they are looking for

Hi- I am new to this site. I am a long-time professional artist getting into the stock illustration industry to earn some extra income during these wild times. After poking around sites like GraphicRiver and other popular stock sites (I was accepted to ShutterStock no problem), I created some assets I thought would sell, starting with some watercolor crystals, noting that the watercolor style was popular and crystals are trendy design elements.

I submitted two items just to get started and familiarize myself with the process and have more items to upload, but after both were rejected, I need to figure out what I did wrong before submitting anything else since they are all similar. Going to put together a set in the near future.

Here is my big question—I did NOT create a help file. I assumed that was for products that require some technical knowledge like an LUT etc. I didn’t know what to put in a help file for a single JPEG or PNG. For a set I could make a directory explaining where to find items but what to say about a single JPEG and PNG except to note that the PNG has a transparent background, but I put that in the description on the page. Do I need to make a file explaining what a JPEG and PNG are or is there really a quality problem?
Here are the files. Amethyst is most recognizable but Labradorite is a very popular crystal too. I submitted these as illustrations under Object and Nature. This is there preview size. The files real files are 3000x4000. Thanks for your time. I’ve been in the arts a long time and am not thin skinned in a critique so if there’s a problem, just lay it on me.