Because there's no one else to wag it for him.
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
A cartoon.
or
That's proprietary information. The answer is available from AT&T on payment of license fee (binary only).
or