Why can't i find a buyer for my 5S???

Hey everyone

I've been trying to sell my 5S in space grey, its 64gb with AppleCare Plus on ATT. No one wants it. I don't know why. I've tried Swappa, Amazon & Ebay. Dabbled with Craigs all for around a month. I don't think i could give it away. I was asking 750, and its new and I never used (apple just swapped it) it but all I get is these low ball 450 offers.

AppleCore why do you think this is? Do people not want the 5S? Im struggling to find a good reason!

(also im not trying to sell anyone on the core anything I just need help finding out why I can't sell this thing!)