Your asking for a reason why. Yet you already have your answer
"isn’t at the quality standard needed to continue forward with the review process"
I’m sure you put a lot of time and effort into it.
Putting some of the mistakes you have made aside, it simply isnt good enough. you have white outline missing on group c. the cut off corners are all facing same way. is it good enough to go on someones wall/tablel , yes it is, is it good enough for graphicriver no it isnt.