The fact that 1x1 is flooded with romance RPs, and is known for that and its tendency to push or destroy the boundary for explicit sexual content, probably creates a vicious cycle where people there tend to look for it, and other don't bother looking. I know the couple times I've glanced through, I couldn't spot an RP that wasn't focused on a pairing.

Put the idea in the general interest check, and advertise it specifically as not AxB. That gives you a better chance on the audience.
If that doesn't work, you'll have to find a player you get along with that's willing to do it.