Perhaps you can clear this up

[urban dream]

uhh not exactly a watcher of the show myself. so no i dont know...yah

Well, Gatomon was introduced as an evil character and only became a goodie after a couple of episodes, when she rebelled against her evil master. It was then revealed then that she had been beaten by that master -- Miyotismon -- for years. So Gatomon unites both bad girl and helpless victim, standard characters in the sexual fantasies of many males. I think this explains her popularity, and I think it might be something similiar with Renamon.