There are several potential explanations for why men may have an enhanced brain response to erotic images. One possibility is that men have a stronger biological drive to seek out and reproduce with a mate. This drive may be reflected in a stronger response to sexual stimuli in the brain.
Another possibility is that men and women have different patterns of brain activation in response to sexual stimuli due to cultural and societal expectations and influences. Some research has suggested that men may be more likely to view sexual stimuli as a means of achieving pleasure, while women may be more likely to view sexual stimuli as a means of obtaining a relationship or achieving social status.
It is important to note that these are just some possible explanations and that more research is needed to fully understand the underlying mechanisms behind brain responses to sexual stimuli.