Why were all three photos rejected but accepted by other stock agencies.

These have been accepted by Getty!

By @Bhupinder_Singh2178

That's of no interest to Adobe stock. Every agency does its checking according to their own rules.

Short Eared Owl Dive:

It has exposure problems (underexposed), it is not sharp, and it has been processed in a strange way that does not make it a naturally looking picture.

Dalmatian Pelican Flying Dawn Kerkini:

This one is extremely underexposed:

And there is a lot of noise.

Dalmatian Pelican closeup Kerkini:

This one is extremely cropped, but I am not convinced that this is the main refusal reason. The refusal reason is the massive noise that is present in this picture.

(seen at 100%)

Adobe does not accept noisy pictures.

It's unfortunate that the beak was cropped in this one - shooting in vertical orientation would be better.

Dalmatian Pelican closeup Kerkini.jpg

The second one is underexposed and the third one was poorly cropped. Adobe is pickier about those issues compared to other stock sites. At 100%, the feathers of the owl aren't sharp..