I believe the rise of these kind of movie "reviewers" comes from the fact that many films nowadays aren't simply good enough. When something is great, it's hard to put an argument against it. When something's awful, it becomes easier to shit on it.

I'm inclined to believe we live in an era where audiences have seen a lot more movies than previous generations. Whether they have seen the good stuff, that's another matter entirely. A very interesting topic for debate which would probably need a whole podcast!