looking for constructive feedback on why these were rejected and how to improve in the future

Bee:

Very noisy and the bee is out of focus:

 I don't even see anything in focus. You could have opened the aperture quite a lot, to get the ISO down.

Pelicans: out of focus and noisy:

The histogram shows missing whites:

Both photos have too much noise and are too soft. The second photo the tree should be removed.

Noise reduction and sharpening are needed. This can be done in post production.

Please remember, Adobe Stock is not there to teach us how to make a perfect photo. They are there to market our photos. We must deliver a quality product or they can not market it.  This forum is provided to assist contibutors who may need assistance.

Well yes. I was getting the same "umbrella" rejections lately too, until I stopped uploading : ). Problem solved!(?). I tend to believe Thai it means not so much the quality (technical) of my/your photo but Adobe hinting that there are already a million of this subject posted (,better ones than yours or mine) and no point in adding more. But this is just a hunch. To me your pelicans are a bit underexposed. And what is that bump on the beaks? The bee one is all right, just millions of better ones up there. (More details, etc.). And I do t think this is a commercially very lucrative subject. Just my 2 cents worth. But I agree! The "quality issues" is just way to vague and annoying "reason" to bump you off.