Romero created something that is actually quite special. I love (LOVE) zombie movies, and NotLD is still amazing. But watching the original Dawn of the Dead and especially Day of the Dead, they seem incredibly dated.
Part of that is the development of make up and SFX. Part of it is just in the nature of movies.
So you get folks like Gunn who decide to “reimagine” Dawn of the Dead. You end up with a good zombie flick, but purists get mad that they run, or that they used the title and premise of a classic and didn’t follow it exactly. Then the studios, seeing dollar bills, greenlight the Day of the Dead remake, and 28 weeks later, and other zombie(ish… the 28 days movies are not really zombies, but I’ll give it to them) movies, and you end up with some TERRIBLE movies.
Meanwhile, you get Romero trying to recapture that flame in Diary of the Dead, a good movie but a bit heavy handed. I think he’s done now, which is sad to say probably best for the genre.
To sum up:
Flooded market creates glut of bad movies. Zombie movies that are not derivative of earlier works is going to be hard, because really, there’s only so much you can do that isn’t variations on “hole up in a building and hide from the zombies”.
The flip-side is, you get movies like Fido, which is BRILLIANT. But they are few and far between.
Someone out there has a fresh, original script, with good ideas and a great eye for movies. But he’s not getting his movie made, because the studios are just about done with this wave of zombie movies.