I think one of the problems may be that it is an open server. A 10-year-old could get on and start posting random things, or somebody could post inappropriate content. It is hard to have a conversation with someone on Discord when a couple hundred people are all posting at the same time. Also, many people may find Discord a lot harder to use than the forums. The forums are simple, but Discord has many more features and buttons, along with the advertisements for Nitro.
I only have two social media platforms on my phone. One for contacting family because my service provider sucks, and another that I have for the information, and also for contacting people. I'm not getting Discord. It takes up too much space, I'll have to give them my e-mail, make an account, get thousands of notifications (even though I can turn them off, I'm trying to be dramatic lol), and it's overall just a negative experience.
They better not get rid of the forums.
Edit: Like
@Johnny B. Goode said, if they do remove these forums, I will probably also leave. The community on here is *mostly* great and helpful, and it's fun to come on and talk about the game. The game itself is fun, but it is based off of the relationships players have. You are codependent. Without other people, there is no game. (There's actually a game called There Is No Game. But this is FoE. It's supposed to be one of the best games out there)