Because it isn't a tennis ball?Well there you go. Plenty of it to be had.
Why didn't they just sneak a bunch of tape onto the ball back yard cricket style?
I bowled a red painted golf ball once in an interschool match. First ball of the game. Batsman, keeper, slips all hit the deck because they lost sight of it. Bowled mid pitch and it damn near made the fence on the full. Oddly it was the only ball I bowled in that match. And I didn't field or bat either. Unfair really 'cause the guys who bowled apples and tennis balls didn't get suspended.