Why is Lord Vishnu holding Goddess Lakshmi's breast in ancient sculpture?

Why is Lord Vishnu holding Goddess Lakshmi's breast in ancient sculpture? They are husband and wife and romantically love each other. Did your parents not teach you what this entails? From the ancient Shilpa Prakasha text, written by the very sculptors who made such carvings (specifically the great sculptor Ramachandra Kulacara): “In this context, hear the rationale for erotic sculpture panels; I will explain them according to the received tradition among sculptors. Kama is the root of the world's existence. All that is born originates from Kama, it is by Kama also that primordial matter and all beings eventually dissolve away. Without the passion Shiva and Shakti, creation would be nothing but a figment. Nothing from birth to death occurs without activation of Kama. Shiva is manifest as the great Linga; Shakti’s essential form is the Yoni. By their interaction the entire world comes into being; this is called the activity of Kama. Canonical erotic art is an extensive subject in authoritative scriptures; as they say, a place devoid of erotic imagery is a place to be shunned. By Tantric authority, such places are considered inferior and to be avoided, as if tantamount to the lair of death, of impenetrable darkness.” - Shilpa Prakasha 2.498–503