I've played on a couple of Call of Duty: Zombies-inspired servers myself, and they're fantastically well done. They replicate many maps to the finest details, have a massive array of custom weapons, and the game genuinely feels like Call of Duty. With that being said, to develop something of this scale would absolutely kill the developer team's schedule for weeks, and honestly wouldn't be worth it. Due to the mass amounts of entities on screen at one time, the size of some maps, the texture pack requirement, the mods, etc. the game would be laggy enough that the majority of the player-base wouldn't be able to play it, even if they wanted to.
"But Hypickle has it" - Everyone
Not. An. Excuse.