Pictures rejected due to qualtity issues

Stock sells assets for use in commercial projects like product packaging, TV & billboard ads, marketing, & merchandise.   

This is what you're competing with in Stock inventory. 

https://stock.adobe.com/search?k=astrophotography

I'm unable to open attached files. This forum's viewer is broken. 

The moonshot is underexposed. You should modify the moon's exposure. I think you have masked the moon, but it is not perfect, so when I modify the exposure, I get a kind of ugly halo around the moon. 

The sunshot is underexposed, too. And it has indeed grain and colour banding.

The deep sky image is also having exposure issues, you should modify the blacks and the highlights and the whites. You could start with adding some contrast and structure. 

I think you could address the issues, by carefully editing and masking what needs to stay untouched. Your pictures are quite impressive.

As a side note: the categories are useless. They have been grandfathered from Fotolia, but there is absolutly no discernable use of those. 

Ditto what @Jill_C said, but I can understand where a less than experienced moderator might consider the "noise" to be excessive in the third image, while that same moderator may have a personal disliking for square formats (no room for a buyer to crop or add copy, though any competent graphic designer would be able to adjust the image as needed). But the rejection of the moon image stumps me completely. For what it's worth, I've also had at least a slight increase in assets rejected for quality issues where I could find nothing amiss.

The rejections can at times be unreasonable and unfounded. I don't know what criteria Adobe Moderators use to judge such images, but they look good to me!