Not being poly and only a bit rational (so far), I’ll only propose
Is polyamory actually higher amongst LW people than the general population? Do you just have more exposure to polyamorous LW people than a wider polyamorous population?
Do polyamorous LW people talk about their polyamory more than polyamorous non-LW people?
Meta: I really like the three top-level comments you made to structure the conversation. Is this something you came up with, or perhaps picked up elsewhere? Does it have a name?