Because it's demeaning and meant to meant to be degrading. Women are often depicted in positions like that of animals with their private parts exposed, or as children or mere objects. Very often they are portrayed in violently suggestive situations, like with someone pointing a knife at their genitals, or tied up with ropes.

It's very much like the old Mistrel shows where blacks were put up on stage in humiliating skits with costumes and makeup to exaggerate their african features, while the crowd would leer and jeer and make fun of them.

It takes the most vulnerable expression of love and turns it into a mockery.