People like to party and have a good time. We're all human. So what?
There used to be a swingers club in Portland. Last I heard it was shut down but maybe they reopened, Ron Jeremy was part owner. Members only, but membership could be purchased at the door. Mostly regular people as far as I could tell from the one time I went.
I've met several polyamorous people in the Northwest and the Midwest. It's not that unusual.