Hello!
My first mockup was rejected today, because " it isn’t at the quality standard required to move forward".
Also, why wouldn’t I be able to re-submit this item again? Does it mean there’s no point making it better and fixing the problem?
I used a photo on a white background, that I took some time ago.
https://postimg.org/image/6md7bfzhp/
Could you please have a look at this rejected item and help me understand where did we go wrong? 
Thanks…
I’m sorry that your item got rejected. It happened to me too many times as well. Basically what they are doing is giving you the finger and leaving you clueless. These forums are no help either.
I for one like the logo though!
Hello there:) First things first - did you name layers properly, made it all clear and readable?
About the design: I wouldn’t use so much of pink in the preview (even though I’m a girl that loves pink). You should also include more versions of the mock up - like the front, back, different angles or such.
Even if it is in the package - show it in the previews.
Also does this mock up have high resolution? It has to be all perfect, since the marketplace gets more and more crowded everyday.
There were few times when I bought a product here on GR and when I unzipped it and tried it - it had quite poor quality, which makes me think if a good preview, help file and well-written description isn’t the key to getting accepted. Ahh, anyways I hope I shined some light, if not - just experiment and see what gets accepted 
Envato is a raffle. You have a 10 to 15% of getting approved regardless of your quality.