It may be because the design is way to simplistic, and does not have too many elements at all. Besides the yellow gradient shape at the bottom and the text + the logo there is nothing else present on the design.
Try to spend some time on Graphic River and analyze what people upload and what designs get approved. You’ll see that most designs have something extra, a little bit more shapes, some more color, text aligned in certain ways, etc.
Spending time and learning from other people can help you a lot and will eventually get your items approved. Try to find some business card tutorials on Envato Tuts and try to build one. It may help you see your mistakes.
There are A LOT of people uploading (or who already uploaded) a lot of business card packages and in order to get your package approved you have to do something pretty good, so keep that in mind before submitting anything.
Thank you The_DrX