It sucks for search engine indexing and it sucks for providing support for stuff because the conversation moves on before anybody who might help will see your query.
One simple solution to this would be a Discord bot that publishes a log of all messages in a channel to a website, thus making them indexable by Google. This used to be common practice for IRC channels and you'd sometimes find an answer to a programming question in the published logs of some IRC server.
Of course, an even better solution would be for Discord to offer this natively to server admins. Give them an option to make their channel indexable by search engines, and then mirror all the posts to a subdomain. It could even be a funnel for Discord since they could get new users to signup when they land on an answer and need to signup to ask a follow-up question. It could also be a wedge to compete more directly with Reddit.