Google can index other forums, like our own. Or stuff like Wikipedia. If Reddit doesn't want to be indexed by external search engines, then they gotta build their own or be unsearchable. Their existing search system is abysmal.

Reddit becoming unsearchable would really damage their usability as a forum site.

You can say that even if Reddit's value as a forum falls off, they kill the goose that lays the golden eggs, they can still sell access to their existing forum archives for AI training, but those have been archived and are downloadable online, at least up until early in this year. I mean, there are gonna be companies running AIs trained on that in jurisdictions that Reddit cannot sue them in and don't care about honoring US IP rights, like Russia.