The common theme is "publicly visible sex stuff that traditionalists and conservatives persecute". LGBT covers most of the people interested in a coalition agai

The common theme is "publicly visible sex stuff that traditionalists and conservatives persecute". LGBT covers most of the people interested in a coalition against conservative sexual mores. The BDSM/kink scene is something that is much easier to keep private, and polyamory is small/private enough too. Heterosexuals interested in per-marital sex have basically won their fight, so they're less interested as well.