Why this picture not meet the Adobe Standards

It's not an illustration.  It's a photograph.  The photo requires post-editing skills in Photoshop or Lightroom to make it suitable for commercial use. 

Read these links:

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
• https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
• https://helpx.adobe.com/stock/contributor/user-guide.html/stock/contributor/help/photography-illustrations.ug.html
• https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html

To me it looks like a photo. If you wanna make it an illustration, do so but it can't be marked currently as a illustration as is.