Here's why:

* Projectile Motion: When a ball is thrown, it follows a parabolic path due to gravity. This is called projectile motion.

* Horizontal and Vertical Components: The initial velocity of the ball can be broken down into horizontal and vertical components.

* Horizontal Component: The horizontal component of the velocity remains constant throughout the flight.

* Vertical Component: The vertical component of the velocity is affected by gravity. It slows down as the ball goes up and speeds up as the ball comes down.

* Maximizing Distance: To maximize the horizontal distance (range), we need to maximize the time the ball stays in the air. This is achieved when the vertical component of the initial velocity is at a perfect balance, allowing the ball to spend an equal amount of time going up and coming down. This balance occurs at a 45-degree angle.

Important Note: This is a simplified explanation assuming no air resistance. In real-world scenarios, air resistance can affect the optimal launch angle, making it slightly less than 45 degrees.