I’ll venture a guess. Mainstream politics (in America at least) has become something of a spectator sport that leads to unproductive, irritating, and dysfunctionally polarizing behavior.
Sure, polarisation may exist elsewhere, but does that mean we have to bring it here too by talking about it? (Because the users on HN are subject to the same tendencies as everyone else, and almost invariably the kind of conversations that polarise elsewhere will polarise people here too.)