A reason is actually always mentioned, such as technical reasons. With your photo, I think the subject is not interesting. Here you can get tips for better images: https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html?set=stock--fundamentals--adobe...
Hello @Miss photographer , you made a mistake that most photographers make. Your highlights are overexposed and your shadows are underexposed. This hides or eliminates details in those areas. When I darken your photo I see clouds on the horizon that your photo does not show. They can be brought out in post pprocessing. Such as with Lightroom. Normaly, you should expose for the sky. Even better take 3 or more photos exposing normal, -1 stop and +1 stop. Then combine the photos in a HDR program. Your photo also lacks color and contrast. I edited your photo which I believe make it more appealing. I removed and replaced overexposed areas, lightened the shadows and removed distracting obects. I also added contrast and saturation and a light flare where the sun shines through the leaves.
If you are new to stock, you should consider these resources: https://helpx.adobe.com/stock/contributor/tutorials.html
Please read the contributor user manual for more information on Adobe stock contributions: https://helpx.adobe.com/stock/contributor/user-guide.html
See here for rejection reasons: https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
and especially quality and technical issues: https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
Your image is gray and dull, lacking contrast and color, which makes it unappealing. Including just a few branches rather than more of the tree is also not an appealing composition. You could have backed up or repositioned yourself to include more of the tree.