I think it’s likely really surprising to learn/experience that feces of a breastfed baby (and to a lesser extent formula fed babies) don’t smell like shit. It’s natural to want to share a surprising learning. Might also be good to be forewarned the milky smell ends once normal food is introduced.
The usual interpretation is the director was trying to move the plot along with things happening during the sex scenes, but the penis was so attention-grabbing that the audience missed the plot points, which made them struggle to follow the rest of the movie (be confused).