what is the canonical reason why they don't use guns here

ok so before anyone says, yes i know the real reason why, its a lighthearted kids game and whatever but just hear me out here

there is no reason as to why the humans should use a gun over a peashooter

-a peashooter or any other plant will **eventually** kill a zombie

-there will be a said zombie used to counter that plant and vice versa

-it would be so much easier to kill the zombie with a bullet the size of my pinky finger traveling at 2,7000 feet a second