Modern chat apps & message boards use their own image hosting rather than people sharing links. A bunch of old message-boards are going to be full of dead links though. Hosting these old images probably cost a ton of money that they don't recoup, whereas new users pay for their storage by forced app download & giving up their data.

And they'll probably save a lot of money. It's not Tumblr. It's an image hosting site that allows deep links to images uploaded by free users. It's, by definition, not sustainable.