OK Nitpick time.
1. Convenient, isn't it?
2. Because he's nuts.
3. Maybe he was aiming for the head and missed.
4. Because he's nuts.
5. (reason for booby traps) Because he's nuts.
6. Because he's-- oh, right.
I'm not sure all zombies know how to turn doorknobs. Morgan's wife was doing so because they appear to retain a little association with some things, and that was her home.
Umm.. Because heís nuts doesnít cover it, you donít set up all those elaborate traps, have a mass storage of weapons, have a system for clearing out the town, finding food and so on and then claim ďBecause heís nutsĒ.
If he is that nuts he would just eat a gun.
The house Morgan and Duane was in was not theirs, I would think retaining some memory how to do things would apply to most zombies, there was 10 plus in the bar, none of them retained the memory on how to open a door?
Again one of those things that drives me nuts, Carl can shoot a hair off a gnatís @ss in dozens of episodes but all off a sudden he misses Morganís head from 10 feet away and shoots at his chest?
All of our heroes for that matter can get a head shot from 30-50 away on a dead run, from a moving vehicle, through chain link fences and so on (with a pistol no less) but when a character is not supposed to die they canít hit the broad side of a barn.