Some of the photos have been rejected due to "quality issues." Help to determine what exactly?

The grass photo is a hard sell due to too much competing inventory.

https://stock.adobe.com/search?k=grass+field 13.5 million results.

Read your Contributor User Guide for more tips:

• 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/contributor/help/how-to-submit-distinct-content.html

Underexposed in the shadows. The moderators review thousands of photos per day and simply are not granted the time to provide precise details as to why assets are rejected. Not to mention that many images have more than one issue, which would require even further time to explain.

Lake in mountains landscape nature.jpg - DOF is definitely too shallow here, and even the row of grass that should be in sharp focus is a bit blurry - probably due to the wind.

Lake in mountains landscape nature.jpg - there's a halo along the edge of the mountains and a blownout spot in the lake of the far right.