Zombies are... cool?
Rotting undead legions determined to do nothing more than devour human-flesh? What's not to like?
They don't have enough personality to be ruined as monsters (unlike vampires, werwolves, etc. which all have a human side to them... WHY CAN'T VAMPIRES JUST BE EVIL LIKE DRACULA!? WHY MUST THEY BE TORTURED SOULS OF THE NIGHT!?!? RAAAAAAAAAAAAAAAAAAAAEEEEEEEGG!!) and are pretty much the final solution to the perfect race of beings. Unthinking, unfeeling and undying. Creatures driven on impulse alone... You can vary them as much as you'd like as long as they're undead (or inhumanly impulse driven)killers. Far as I'm concerned the "infected" and necromorphs are all zombies by a different name. A zombie is suc a blanket term these days and that's fuckin' awesome.
I find people who dislike zombies generally just try to box the term in with Romero-esque flesh-eaters slow, stupid and dead. I find a zombie is just anything driven by a single impulse that, at once, had a rational thought process. Be the impulse "kill", "eat", "infect" or "dance", if that's all it can think about, all it can do, then it's a zombie.
Zombies are the perfect monsters.