There may be other problems, but the trademark issue is very clear. All "Olympic" themed items in Stock that I found are under the Editoial category. You can no more make a graphic and sell it commercially saying "Olympics" than you could make one saying "Mercedes" or "Coca-Cola".
It's a strange question originally... we are being asked for possible reasons, but if the image was rejected, then a reason was given. This leaves us to guess... so, GAlexS, if your design was already rejected, please tell us the reason. It will save time for you and us.
I see where "Olympic" is trademarked, not "Olympics". I also see where it says that trademark words can be used in a factual way. My suggestion is, if the asset was not rejected for copyright infringement to do the other corrections and allow the moderator(s) to make the decision.
That is a beautiful vector art. From where I sit I am unable to say what the problem is. That is because most of the times the rejection reason may be a technical issue such as open path, or failure to organize and label layers. Therefore, what I'll do is to give you a link that will give you an overview of what you need to check for. You can read through and compare with you work in illustrator.