It's a comfort thing. Autists always retreat into fantasy and anything that makes them feel comfortable, which is why they love nostalgia (don't know why I'm saying "they" as if I'm not autistic )
So, if an autist in the TF community grows an attachment to an inanimate object at a young age, it's most likely because said object made him feel very comforted, and safe. Eventually this fixation with comfort becomes associated with sexual pleasure once the autist discovers masturbation, and the autist will start linking this personal fetish of his with his natural attraction to humans. And then we're left with this.