Porque esta foto me fue rechazado?

You need better lighting. See Histogram panel.  

HINT:  Food photography should look appealing. You might want to scrub potatoes and brush a little vegetable oil on the skins to improve their visual appearance.  Some food photographers paint food with thin pigments.

Compare yours with current Stock inventory.

https://stock.adobe.com/search?k=red%20potatoes

Good luck.

Depth of field is too shallow, so very little is in focus. You also have a few spots in the background.