This is almost inevitably caused by the fact that all the promos you are running are using promo codes.
Detailed Explanation:
Whenever you create a promotion, you have the option of adding a promo code. As a reminder, this code is used to limit the promotion to only those customers that you have given the code to. They can enter this code during the checkout where it asks them something to the effect of ‘if you have a promotional code, please enter it here.’ Since this promo code is secret per se, (limited to only those people that you give it out to) then you would not want to advertise this on your promotions list. If you really wanted to display a promotion code somewhere on your site, you would need to hard-code it (add it manually) to your website.