>How is it that in most breast expansion comics there rarely is a fucking sex scene?
Because usually the comics are made by breast expansion fetishists, who care more about breasts getting bigger than sex. A good part (30% maybe) of newer BE stories barely have any sex.
Used to be a bit different in the past - old stories have sex and typically also some remarkably blue-pilled ideas about romance. But newest ones are probably made by people who rarely if ever have sex, or orgasm much more to BE content than sex.
From the point of view of their brain, jerking off is sex. You are what you do, it's always like that.