Then you really shouldn't have bought the game.
The durability acts as a balancing scale to keep you constantly changing weapons and trying new things, plus keeping you from getting too overpowered by stockpiling loads of uber weapons.
It's part of the game's mechanics, and the game is built around it. If you don't like it, buy another one of the 50,000 zombie games on the market.
Man I am sure getting sick of this entitlement some people tend to have about game mechanics, thinking everything has to be designed just for them and the way they want it or it is wrong. It's the same type of thinking that turned Dead Rising from an interesting spin on the Zombie genre with its own genuinely unique mechanics and rulesets to a super generic run of the mill grimdark action game "for the call of duty fans" with Dead Rising 3.