And the very features that makes forums desirable require good moderation, while on Discord a toxic community can be left mostly unmoderated due to the semi closed and transient (in appearance) nature of the chat. Having the same on a (google) searchable forum that make it easy for people to find and see the toxic content would pretty soon result in demands for better moderation.

I find it sad that this is the reality we live in, but from a business perspective I can kind of understand it as the target audience of these gaming websites can be quite toxic.