Working together to survive is a complete joke. The zombies are a non-issue basically after you've crafted your first wooden club. PvPers like the danger of another human, and it makes the whole dynamic of the game more exciting. It makes base building even more interesting and people who like elaborate base planning, traps, decoys, raiding, detective work, reverse-engineering, and figuring out ways to exploit others' constructions have a blast in PvP even if the game doesn't properly support it.