Sure, just show me the combined DnD/D&D or TTRPG community | magazine | group. It doesn't exist. There are a hundred, or a thousand, individual groups. That's not a whole community. That's a thousand fractal shards, each one with its own voices, independent of one another. Yes, occasionally they do share content or users, but that happens only rarely and with effort. TTRPG Network, Lemmy.ML, KBin.Social, Mastodon.Social, etc., all have various groups dedicated to RPGs. These groups are not able to be combined.
The inability of these groups to combine and independently organizing is a severe weakness of ActivityPub.