Why so some people believe in zombie outbreaks?

You are not paying enough attention to understand what they are saying.  They main cause is almost over with so many getting their vaccinations.  But being prepared for an extended period of time, one needs to stock up on things they need just to exist.  Most people are followers & will follow whoever leads them.  Fears go hog wild, logic left the room, NEEDS take priority.  Stock up on things that one would regularly run out of.

Some people normally keep a full supply of regular needs, while others only keep the basics.  Those who only keep the basics are usually the ones that go hog wild stocking up on everything.  There are kits that one should keep handi in a time life now.

It's the same fear of the unknown that made people terrified of corpses, thunderstorms, and eclipses thousands of years ago.  Gullible, paranoid people who don't know for a fact (in their minds) that corpses can't come to life and wander around with a hunger for brains turn that lack of knowledge for one thing into convinced knowledge of the opposite.

They can not get their mind off a movie.

Their heads are stuck in the zombie movies. They don’t think outside the box (literally the tv or cinema screen) and that the viewer believes in the zombie characters played by actors. They are just being foolish. Personally I like zombie movies but I know that they are fake and I think outside the box.