What is wrong with the quality of this picture?

In addition, you should not submit PNG files, if they don't have a transparency.

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

If you are a generative AI contributor, please look into these instructions and follow them by the letter: https://community.adobe.com/t5/stock-contributors-discussions/generative-ai-submission-guidelines/td-p/13549435

The image is underexposed with some blown highlights and not sharply focused. You also submitted in png format, and it should be jpg. Don't even bother with submitting photos of plants, unless it is an exotic, rare species. Adobe is overrun with flowers, trees, plants, etc. as these seems to be the preferred subject of beginners. Look for more unique subjects, and read ALL of the Adobe Stock Help pages.

https://helpx.adobe.com/support/stock-contributor.html