The love of games is the main topic and the glue, but I've always thought that gaming overlaps with fantasy, sci-fi, creativity, storytelling, sportsmanship, etc., so one common ground for me implies some others.
We've been the weird ones just until yesterday. Now all media, money, ads and, luckily, approval and pop culture is
with "us" since technology and computing and even elves and the like are "mainstream" (mainly because tech has spread and has become an everyday thing both for good and bad). And we fractured in "I like this", "I like that" (and is still games and gaming mostly, i.e. when real world does not get thrown in too heavily and in a copy-paste, unthoughtful way). Like rockers or music lovers some years earlier. A bit more guitars and a scream VS a bit less guitars and a synth?!
It's a broader trend, I think: to be better in showing off "allegiance to" something and raising a flag (even a flag of a "colour and shape" surprisingly similar to the ex-friend's) instead of enjoying on par. It's not challenge ("I made a better level, try it") but competition, and it's quite supported by channels, tvs etc. ("There can only be one new level, mine or yours")
So it's rivalries, seldom artificial. "Long live Unreal!" "No! Long live Doom!"
Difference being 10% (how they tweak some design or how they program an engine to do the same thing in a similar gaming purpose)
Really?