What's the problem with Nashor's Tooth on Twisted Fate?

Overall, it looks like he'd benefit from it greatly. The Attack speed synergizes with his E, the cooldown reduction, all of his abilities, the AP, albeit small compared to another item, still is beneficial. This is just raw stats, the passive itself seems as if it'd be tremendous on our Card Master. So please, could someone inform me of why it isn't recommended, and, to me, it seems, why it's shunned as a purchase? Of course you wouldn't choose it over the big three or Lich bane, but one extra slot is open to so much possibility, and one of them being this beloved Void Fang. For mana issues, sure, yes, besides Lich bane, you have no mana sustain.. Or do you? Cooldown reduction on your W will allow you to throw out more Blue cards in situations that demands it, when low, and need to conserve mana for a W+Q combo, you have sustained damage with your auto attacks and E. So, Why? Why isn't this built on him?