Hi, Tiffany - welcome to the forum! Tell Will hi from me.
I don't think it's that there's something wrong with the deck. The art is fine, the design is solid. The only issue I can see is that the theme is one that's been done before, many times in fact. Maybe it wasn't done exactly like your deck, but it was done in the same vein, making your deck look close enough to some of the others to lose differentiation. The problem with treading on familiar ground is that if you aren't doing it an order of magnitude better than what came before, it's difficult to stand out from the crowd.
It's also a little bit short on the "bells and whistles" that draw collectors looking for the rare and exotic. The prototype shows a custom deck seal, but that appears to be all - no fancy foil work, no die-cut windows in the packaging, no metallic inks, no UV inks, no holographic cellophane, no glow-in-the-dark, nothing. Aside from the custom art, it's as bog-standard a production as you could make of it. I'm not a big bells-and-whistles kind of guy, personally, but some collectors seek that kind of stuff out like bugs at a klieg light.