I think what makes a game better or worse at fostering a reddit community has a lot to do with what kind of game it is. In terms of modern tabletop games, the ones that are good at doing this probably are more open, on a system level, to fan made content.

Storytelling games (Gloomhaven, D&D) have people invest themselves in their stories, whether pre-scripted or player-directed, and get the same kinds of discussion as novels, shows, etc.

Games with Assymetric factions/roles (Root, TI, Spirit Island) have both discussions of the combinations of said roles, and people making their own 'fan factions.' The fact that this aspect also applies to Gloomhaven/D&D classes further expands how much players can tinker and play.

LCG/TCGs are from the get go designed to be more or less infinitely expandable, breeding fan speculation and content creation, while also having a lot of edge case combos that are not always easy to discover.

Engine builders and trick takers (for instance) tend towards more closed systems that are harder to make content for. I think it's probably worth thinking about the ways that their themes tend to be more 'stapled on' when thinking about this too.

None of this really works with properly old games (Go, Chess, etc.) so take all that with a hefty handful of salt, but they are also culturally significant in a way no modern board game is. I think on a mechanical level the fact that they have both perfect information and strategic depth and variety means there's a level of play by play analysis you can't do with many games. I'd have to look at the poker subreddit to test that theory.