I always assumed that it was so they could manipulate and open jars.
I assumed that scratching their balls was dangerous and diminished their gene pool.
Chickens are today’s T-Rex’s.
T Rex Eats Lawyer
https://www.youtube.com/watch?v=VMzfrod7hcE
Cat catches mouse, it escapes but chicken grabs it
https://www.reddit.com/r/BackYardChickens/comments/1q0gak5/wait_for_it/
Chicken Steals Mouse from Cat
https://www.youtube.com/watch?v=Mwy4X4F3mB4