Because he saw the salad dressing!
or
To see how long he slept.
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
How dare you be so intolerant! So what if the light bulb has chosen an alternative light-style?
or