Please help me understand why this image was not accepted

Colourful cereals are unhealthy.

Besides this, some serious arguments, that may have led to the refusals:

Your planks should be consistent.

I do not see an optical reason, why the liquid is out of focus and the cereals on the same plane are not, or the inverse.

The asset I've seen is 1024×1024, which is hell too small for Adobe stock.   But still, I can detect in the background a bad cut-out bottle and a reflection, that is too sharp.

This looks super synthetic to me.  That's usually an indication of more than one problem with perspective, geometry, light source, shadows, reflections & details that don't make sense. 

Did you pay extra to generate high-resolution diffusions?   If not, you need to.  Low res JPGs won't be accepted by Stock.

Carefully examine every part of your image at 100 - 300% magnification.  Fix all imperfections if you can.  If you can't, just discard it.  In my experience, only 1 in 10 AI diffusions are worth keeping. 

Overall it's quite fuzzy / unfocused. There are also geometric issues with the seams in the tabletop. The light is inconsistent. It comes from the back of the bowl, but also in front of the splash.

Forive me, this was supposed to be included with my reply.

Greetings!  I took a deep dive into this photo, and here is what I noticed.

-The Histogram reflects underexposure

At 100% view, I noticed some aliasing and artifacts around the edges.  I also noticed some artifacts on both sides of the image that didn't appear to be a par tof the "explosion" to me.  I believe this started at a very low resolution and was upscaled, the cereal appears to be oversharpened.  The table appears to be affected by lens distortion, but the cereal bowl doesn't.

Don't get me wrong, this illustration is cool.  But from a technical perspective there are quite a few areas that need some polishing up on.

Cheers!