Consider yourself lucky. IMO, they are both too blurry for commercial use.
Examine images at 100-300% magnfication.
I think they both have problems. But if I had to pick one, I think the rejected image suffers from too much light (overexposed). However, others here may have different opinions on why one was accepted and the other was rejected.
To be honest, I think that both photos should have been rejected. Neither of them are focused, which I understand is your intention, but Adobe customers are looking for technically perfect images.
If you are new to stock photography, here are some useful links with information regarding what Adobe is looking for in stock photography.
Best of luck in your future submissions,
They are both quite blurry, and the fact that one was accepted just proves that Moderators are fallible. If this is your bookshelf, or you have access to it, I would photograph it again, perhaps with a tripod so that you can achieve perfect focus.
Why was one accepted and the other rejected? Good question. For me also, both are out of focus. Therefore not really usable.
Both should have been rejected. Focus and exposure.
As a matter of fact: If anyone buys the accepted picture, you will get probably that one deleted, as it is unusable. I agree with all the four gentlemen and the lady: they are too blurry for being used. Delete the accepted one, retake the picture and put it again up into stock. One image will be enough, the second one could also get a "Similar picture" refusal.