Most Helpful Girl
Because women are less visual than men in that regard; they find stimulation from the fantasy aspect of reading erotica, whereas men are more likely to be stimulated by things such as porn.
Most Helpful Guy
Women are more aroused by situations and aspects of a lover which are difficult to portray visually. It's not that they are less visually stimulated than men, it's that the things which stimulate them are difficult for the purveyors of porn to show because they would require skillful acting and directing and a good script. Basically they would have to be quality romance films with actual sex.