That's...probably because it's awful hard for people to drum up sympathy for someone who wants to have sex with children. Even if you have a character who is horrified and ashamed of their attraction and does not act on it, the audience reaction you're most likely to get is "good, they should be" rather than genuine sympathy anyway. Writers don't want to touch that bullet ant nest with a 39-and-a-half-foot pole, and I can't say I blame them.