Why was this image rejected for quality issues?

Quality issues aside, there’s too much competing inventory in the Sunset/Sunrise category. 

https://stock.adobe.com/search?k=sunset 33 million results

https://stock.adobe.com/search?k=sunrise 36 million results

Even if yours was perfect, it would likely be refused for “Similar Content.”

https://helpx.adobe.com/stock/contributor/submit-your-content/submit-distinct-content/distinct-content-submission-best-practices.html

Hope that helps.

Low-quality images taken with smartphones or compact digital cameras may be rejected.

Strong yellow cast and shooting directly into the sun can degrade the image. This would have been a strong photograph in landscape mode rather than portrait.