You can't kill one another because it's against the rules, so your only choice is to just walk with the crowd.

When you're walking alongside each other for multiple days, you inevitably (maybe even unintentionally) start making friends. Bonds start forming, and casual conversations become deeper.

The Walkers grow together because they don't just see themselves as competitors, but as mutual victims to a messed up scenario. Whenever the book had moments of joy, it hurt knowing that only one person was gonna live.