These photos were rejected due to quality issues. Thoughts?

underexposed.

_DSC6199.jpg - extremely underexposed

_DSC6205.jpg - more than a full stop underexposed, noisy and not sharply focused

Search for similar assets in the Buyer portal at stock.adobe.com to see what your competition is and determine the expected quality level.

The first is black and white and underexposed, the second too, and there is a lot of vignetting.

The sunglasses are underexposed and not sharp, and the colour is desaturated. There is a yellow stripe in the upper right corner, like a light leak.

Your spider is underexposed, has colour noise, is not sharp (or has a low DOF).

Your cat is noisy (look at your picture at 100%), underexposed (check the histogram) and not in focus (check the eyes at 100%)

I suppose that the rest of your assets has about the same quality issues.

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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