Discord killed forums because people love centralization. Why bother creating an account on a specialized forum when you can just login in into the place where you already have all your friends and stuff? If anything, NexusMod is the prime candidate for it as they pretty much have a monopoly on the modding community.
Not everybody. Discord is horrendous at organizing game info and preserving player base comments. Its great for game play and socialization for those that wish to partake. Some gamers are not interested in that and others CANNOT use Discord because of anxiety or thousands of disabilities that you may not be aware a member of the community has.
Example: If someone asks a question on Discord, the only answer they are likely to get is whoever is on and looking at discord. Otherwise the asker is scrolling back and looking for answers among the other chatter. On a forum, all the answers are in the same thread, and more importantly you are more likely to get answers from people that play at different game times.
A well organized forum will be utilized more often than Discord and is an invaluable resource for game information and conversation. Discord cannot do or preserve this well.
Discord is great to use for in-game party chat. THAT is its strength.
