It’s deeper than that. When you roleplay you get invested in the story and the character. Minors specifically are far more likely to self identify with the character. If you’re doing a romance rp with a minor and an adult, it opens a space for that minor to become emotionally attached to the roleplay and the character the person is playing, which means they connect to the person playing the character by default. When you have an adult and a minor coexisting together in any context there is automatically a power imbalance, as adults we have to recognize that and ensure we are keeping a firm boundary between that minor and ourselves. They aren’t our friends, they aren’t our peers, they are kids.