my illustration got rejected, saying quality issue, please help me understanding my mistakes

Are your illustrations Ai generated?  If so, they must be checked for accuracy by an experienced professional. 

For comparison, this brain illustration was sourced from Physiopedia.

Sometimes, less is more.  

1. IMO, the shadows are an unwanted distraction with so much going on. 
2. I think cursive fonts are a bad choice for marginal annotations. 
3. Global customers will ultimately decide which fonts, languages, and texts if any they need for their project.  Stock sells graphics, not information.
4. This is your competition in Adobe Stock inventory:
   https://stock.adobe.com/search?k=physiology+anatomy

Hope that helps.

​@youthful_Everglow5CD7 
Even though the body has tissue the lines might be bit too blurry. No fault of your own. 
As ​@daniellei4510  mentioned the text, it could be distracting. For the most part, Adobe images have little to no text. This image could be more suitable for other science and biology sites. 

Cheers

Nate

I can’t verify the veracity of all the labels, but it seems that the word in the title should be “perspective” not “prospective”. This is why it’s not a good to include text...

I suppose it could be a little sharper. But personally, I would have submitted this without the text. If I were a buyer and wanted to add my own notations or just concentrate on one or two specific areas, I’d have to remove each and every one of those black lines and dots.