It's not an easy being an Xbox game for Windows platforms. First you have to go through a difficult pitching process just to make it into the portfolio. If by some miracle Microsoft actually approves you for Xbox status, you then enter the equally unpleasant certification process. And once you finally make it to market, you'll probably just get pulled from the Store by Microsoft at some point. You're an endangered species, son.
That's what happened to Zombies!!! for Windows Phone back in September of last year. The game was delisted for having in-app purchases, and then returned in November without Xbox features. The Windows 8 version managed to keep its Xbox features for a time… But now that time has ended. Microsoft recently chose to stop publishing the Xbox Windows 8 version of Zombies. And so developer Babaroga has republished the game as a universal app (but without Xbox features). Zombies!!! has come back to life, you might say.