Because if I didn't use Discord then I would be the only one in the community. Discord has a massive userbase especially with gamers. You give them a Discord link and there's a decent chance you'll see them join and post a message. Give them any other link and they'll never make an account, they probably won't even click the link to see it.

I provide links for Discord, Lemmy, Kbin, Mastodon, Steam group, and GitHub. I see lots of people come in on Discord, but 0 on the others except for myself lol.

Only the few actual contributors use the GitHub, don't think I've ever seen a non-programmer submit a bug report on my GitHub or use the discussions or leave any comments on releases or anything.

I'm also on Moddb and NexusMods, got a few comments on Moddb, none on Nexusmods yet.

I also have Twitch and YouTube of course, I get small numbers of people commenting on those.

Nobody has even asked for any other type of community, Discord is just want they want. If I just wanted to talk to myself then I wouldn't bother creating a community/forum at all.