Why does "rain stop play" in cricket?

There are several reasons.

• The ball becomes damp by absorbing water. This makes it both softer and heavier, so it loses a lot of bounce as well as reliability and integrity.

• The ground, especially the pitch, becomes wet. The pitch in particular needs to be kept dry as much as possible to keep its own integrity, allowing the ball to bounce effectively and predictably. The field needs to be dry to prevent slipping or affecting the movement of the ball.

Playing in the rain would turn the game into a joke, more about random luck than any skill, and add unnecessary elements of injury risk. So it is in everybody's interest to stop play at that point.