Reddit also provides image uploads for free, and most people on discord never use the voice chats as far as I can tell.

It's mostly real-time vs less than real-time communication. Discord for what is worth isn't that hard to search, and I wouldn't mind if they gave the option to some servers to have their logs automatically go to a crawlable page so they'd be indexed by Google. Of course, that won't work everywhere as real-time chats are often also used as they feel more ephemeral.