Can someone help me understand why this photo go rejected due to quality issues?
Out of focus:
and exposure problems:
Blacks (left) are missing, shadows have clipping.
A third reason is the framing: there is some action in the lower end of the picture (1) that take's away the attention and a strange streak(2) which may be an artefact.
Unfortunately, your photo is out of focus - the flower isn't sharp, and it's somewhat blurry. The exposure could also be better which can be corrected in post; the focus cannot.
Focus and exposure are two critical elements in photography that can make or break a shot's quality. An out-of-focus image like your example makes it distracting and unappealing, while incorrect exposure can result in underexposed or overexposed images, which can be difficult to correct in post-processing. You have to pay attention to these aspects while shooting to ensure the best possible results.
Be careful of your background as well.
@Abambo and @ricky336 have pointed the technical issues. I would add that, while practicing your photography and editing skills on floral images is useful and fun, Adobe stock is already completely saturated with pictures of flowers. Even if yours was technically perfect, there is an exceeding low chance that it would ever be noticed or sold. Look for more unique subjects to submit.