Discord is a perfectly good chatroom, but people keep trying to use it for things it shouldn't be used for. It's not suitable for long-term discussions and worst of all it's not indexed by search engines.
Reddit has been slowly decaying for years. The algorithm has been more and more aggressive in pushing memes over discussion, to the point where it's impossible for a discussion thread to gain traction. Even if you could, that thread will fall off and be forgotten in less than 24 hours.