Movie analysis

I ve been watching a few quality movies over Astro in the last couple of weeks. Most noteworthy is a series of zombie movies (hehe). The list begins with ,
1- Zombi kampung Pisang- caused by chemical spillage,
2- 28 weeks- caused by anger virus
3- The swarm- caused by military mutated wasps
4- I am legend- caused by some virus

These movies generally involve human eating zombies.My analysis is as follows ( had I were required to submit a feedback on these movies to my boss, these highly profound observations would be it) :-

1- Why don't these zombies eat one another? Why do they have to eat those who are still not infected?
2- Why is their diet not agro-based? Such as plants, grass and tree barks. In fact it would be quite interesting to see if zombies develop a liking towards eating stones for example, or sand or whatever.
3- Why do zombies develop only a desire to kill people? For suspense and thrill, I can think of a thousand alternatives but all of them escape my mind right now, so I cant (and won't) give any examples.

The conclusion is: I shall change the channel to 108 and will give another analysis of extremely incredible hindi movies I watch on Zee soon. :P