Why?

A question I've always had is why do almost ALL zombie films take place in a world where the mere idea of a zombie has never come into existence? All these films are set in a world EXACTLY like ours EXCEPT for the fact that nobody knows what a zombie is. When the attack first happens you always see a character trying to explain what is going on to somebody else... "they're... the people are... they're biting other people! They're dead but not! People have gone crazy!" Why the hell wouldn't you say, "Holy shit it's like ZOMBIES ARE REAL NOW!" Or maybe you don't want to use the word "zombie" so loosely, but when you shoot the thing 50 times in the chest/arms/legs and it doesn't die, maybe it's time to think, "In the hundred zombie movies I saw, they always said aim for the head so maybe I should try that!" but nope. Shooting them in the head is ALWAYS a new piece of information. 


I think it's just an interesting point and I'm not sure why most filmmakers choose to do this. It's not like me knowing about the concept of a zombie will better prepare me to learn how to use a gun or be able to stomach the blood/pain or find a cure. In fact, wouldn't it be awesome to have a film where it focuses on a group of people who have a Zombie Defense Plan set out already as a joke (but not) and then zombies actually attack? Wait, that's me! Somebody come make a film about me.