To be honest I haven't the slightest idea. If forced to guess, I'd say it was the quasi-realistic wargame simulation of a potential conflict within living memory awakens violent nationalist rhetoric in people? Either way, it's very much not the same as the "your mother" type insults you see in a stereotypical Call of Duty match, it's a whole different dimension of shitposting.

Paradox grand strategy games also have this effect, but that community is better about shutting down their edgelords.