Simplicity of Killing the Zombies

Ok so I guess it wouldn't make much of a show but think of how easy it is for them to just off all these zombies. For example, at the prison why couldn't Michonne just stab all of them with her fucking katana through the fence? If any character can just take a screwdriver and stab a zombie with minimal effort, I feel like they could have just cleared the walls with a half hour of everyone going around stabbing. Plus, in the last episode, when they are barricaded upstairs, why not just stab them when they are behind the couch? In World War Z, the zombies run at super speed and can jump and are scary as shit. But, in the Walking Dead, they are all decaying and slow and gross, yet World War Z at least has a resistance fighting back. The show is really without a direction lately too. There has not been a legitimate villain since the Governor, and besides him it has been 6 seasons of the same speeches about staying alive and boring backstories where Rick is only in like 3 out of 8 episodes in each half season. Kind of getting bored of this show........