Why do male dancers often become the "bottom" of female dancers in the variation of duets?

In the variation of duet, male dancers support and hold up female dancers in many cases; In the overlapping modeling of the two, part of the male dancer's body is often covered by the female dancer, so the male dancer often becomes the "bottom layer" of the female dancer's "picture"; As well as the interweaving of lead dance and group dance, group dance is always the "bottom" of lead dance.