Hello! It is likely because the subject is out of focus/not sharp enough.
Also, the view of the subject is blocked by vegetation. Remarkable shot as it is, Adobe's customers are looking for perfect "TV documentary quality" wildlife shots. They do not consider rarity or difficulty at all.
Portraits, even of wild life, need to have sharp eyes. This one has not (100%):
In addition to that, the picture exposes colour noise and luminance noise at a high level:
Looking the overall picture, you have that annoying patch of something and also some grass crossing the face.
You can't do anything about this, it's there, but it's ruining the usability of the picture.
Last, but not least, the picture is badly exposed. Looking into the histogram
I see that the whites are completely absent and the highlights missing to a great extent.
FYI: the correct histogram for this picture would show something like this:
and the picture would look like this:
Any of those errors would by its own disqualify the image.
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