What a wonderful shot! But Adobe make no allowance for being a difficult or rare picture. The black bird is completely blurred, but from an artistic point of view it is a key subject, and the hawk is not completely sharp. There are artefacts around the edges of the hawk. I form a general impression that this is not a single photo, but a composite. (Composites can be good but they must be perfectly realistic).
I think that the photo may have been rejected because of the sharpness, as well as signs of artifacts. You took this at high ISO - 1600, so because you used some noise reduction, it has also softened the bird a bit.
However, I think you have done a good job of capturing the bird in flight.
For the other bird, you have this: (from the Raven's (?) body artifacts)
I can understand the noise due to the high iso, but it seems to me that you have to zoom in a lot for this detail to be visible and in print it goes unnoticed...
So I will take note for later photographs
Both are shown at 100%!
Adobe recommends that contributors inspect their images carefully by zooming in between 100-200%. The blur of the black bird is readily apparent at even a small size, and the issues with the other bird are noticeable at 100%. Adobe needs to be able to offer their Buyers images that can be utilized commercially in a variety of sizes, not just small prints.
I think it has been rejected due to the sharpness and the noise.
But it is a great shot.