Because a big “Join our community discord server!” on the game’s title screen isn’t enough apparently. They have to put a flashy animated GIF at the top of every update notification, change the name of the game’s Steam forum to “Join Our Discord!”, and even reply to posts in the Steam forum saying “You should join our discord so we can chat about it!” as if a forum isn’t a good place to chat about the thing that’s already being discussed.
Bitch please, if I wanted to be in the hell that is Discord I’d already be there, you can stop asking.
There’s a lot of rationalization there. It was simply the best technical product with lots of killer features when it was rising. People used it because it was the best solution at the time, don’t kid yourself.