It seems to me they exist in a universe where there never was a "Night of the Living Dead" movie so there isn't an already engrained mythology of zombies, including how to stop them. It makes for a better story when the characters don't have a preconceived notion of what a zombie is, how it spreads through bites, and…

They were not four unarmed people. The chick in the video pulled a gun on them as soon as they barged in the room (not saying she didn't have a right to defend herself, just acknowledging the facts).