The body has been jacked in the Matrix for over four years. The diaper is starting to get a little soiled and has a faint aroma of a sweet smelling fart. Everyone wears a diaper when they are getting jacked in for a long term mission. These deep cover operations often forget they are in the Matrix. It becomes more problematic for hygiene reasons alone.
So they call You Diaper Daddy cause you are so deep in the matrix you are starting to leak so bad your have a stink.