Experiencing a huge lose from relying someone else can also teach them a lesson and make them curse those kind of services resulting for them to study on their own. You ask why on discord? But why not? Discord is in fact more rich in terms of features than in telegram and facebook groups/messenger.
I think learning experience from other users is also valuable. You don't have to get scammed to know that a scam is a scam. There's no harm telling people that a signal group is mostly just a scam either. I think the platform doesn't really matter as long as it can provide some notifications, since that's what OP is looking for. Personally lurking in this forum is the best choice if you're trying to learn or read about tech, history, and stuff like that. Discord, Telegram, Reddit communities are mostly created to chase new coins or share trading analysis, which can be misleading if you don't know anything about it.