Here is a quote for an interview with Brad Pitt about the movie...
Pitt said, “Well, you remember that at the time I was really interested in a more political film, using the zombie trope as a kind of Trojan horse for asking: ‘What would happen to sociopolitical lines if there was a pandemic like this? Who would be on top? Who would be the powerful countries and who would be the most vulnerable?’. We wanted to really explore that, but it was just too much. We got bogged down in it; it was too much to explain. It gutted the fun of what these films are meant to be.”
So in other words this Hollywood douchebag thinks people are too stupid to want to watch an intelligent zombie movie, which is what World War Z was - an intelligent book on zombies.
Instead he made the same zombie movie we have seen before, very similar to I Am Legend. In this version he is some kind of genius that the world leaders decide is the only one that can figure out this thing. The movie is an action film. The zombies are CGI and super fast - jumping at helicopters and planes. There may be a battle in Israel and a few other places but it was a total re-write. They even had to cut some scenes that appeared critical of China so they would release it there. Remember in the book the pandemic started in China....
This is like someone buying the rights to Spider-Man and making a movie about Thor.
In another interview he said he wanted to make this movie for his kids. His kids are ....kids, not adults. What he obviously did not do is make a movie for the fans of the book.