Given Taylor's comment about the picture of the Aztec man carrying the unconscious woman, why is the idea that men are strong and women are weak so prevalent? What theme does this issue relate to?

This falls under the theme of the subjugation of women by men. Women are conditioned to feel weak so they can always be controlled and manipulated. Taylor, Lou Ann, and Turtle all discover their strength through their collective love for one another. This matriarchal bonding brings out the strength and resilience of the female characters: this becomes an important theme in the book.