Because having your entire community on one platform is just a hell of a lot more convenient and manageable especially for smaller development studios. And Discord offers way better tools for moderation and real time discussions than any other tool I know.

Sure, the searchability via search engines is pretty much none existent. But then again, you don’t really need that if all information regarding your game can be found via the Discord search.

Additionally, players from all platforms can contribute and ask questions on Discord. The same is not true for e.g. the Steam User Forum.

There’s a lot of problems with Discord and I feel like it’s only gonna get worse now that they’re public. But being blatantly oblivious to the obvious reasons why developers are choosing Discord over its alternatives.