Dogs often enjoy the combination of movement, chase, and attention. The owner throws the ball, the dog runs, the dog returns, and the cycle repeats. It is a simple form of play, but it does a lot.
For many owners, fetch is one of the easiest ways to help a dog get outside, use energy, and enjoy a little more activity during the day.
That is one reason tennis balls remain such a practical choice. They make the game easy to start without needing anything complicated.