It's not because of the resolution. Zoom in to 200% - what do you see? I only see strange color structures. Also the saturation is way too high
Strange, they look rather like a photo of a print on canvas. But surely not?
The second photo, Nature Forest River, has white aberation arround the trees and the hills in the background. Did you swap the sky? Also, like Marianne said, the saturation is too high.
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As you can see from my screenshot, your image quality is not good enough for Stock.
The saturation is way too much!!! It hurts my eyes.