Why does travis kill eckels?

Travis kills Eckels in "A Sound of Thunder" because Eckels's reckless actions in the past drastically alter the future, leading to catastrophic consequences. By stepping off the designated path and crushing a butterfly, he disrupts the timeline, which undermines the careful balance of the ecosystem. Travis, as the guide and protector of that balance, feels compelled to take drastic action to prevent further damage to the future. Ultimately, it serves as a grim reminder of the impact of seemingly minor actions on the larger world.