Because Day Z fans were exactly the sort of people that wanted the kind of game War Z promised, the most likely to have been led in by the lies, and the most likely to have been sorely disappointed by the result?
Regardless of whether it has anything to do with Day Z, it is certainly relevant to the Day Z audience, most of whom (in my experience), were rooting for this game being awesome and were all too likely to fall into it's trap.
I must disagree, i do enjoy dayz and i can asure you anyone with anykind of gaming experience could tell just from seing 10 secs of gameplay that it was nothing compared to it. Even if done right 100% i would still consider it shit, it takes all of the "survival/harcore/simulation?" from the game, storing items between livies in private bases? no thanks, Bandages that heal hp? no thanks, CoD like shooting? no thanks, etc etc etc.