Earlier quoted context omitted.
But Twitter, Reddit, HN, and most other such places are just websites and can be indexed fine. Same with Wikipedia, which is very much a silo (they don't have regular links in text in the hypertext spirit, but only footnotes). Facebook and Instagram are more of a walled garden, like Quora, but there is a lot of junk there anyway. It's sad for the WWW, but I don't really think it is a fundamental problem for search en…
Twitter and Reddit still can be indexed, but they've also become increasingly hard to use without an account. Reddit doesn't let you fully expand threads when you're unlogged. Twitter limits the amount of things you can read and shows a modal. Both of them heavily limit usage on mobile devices without installing an app. Sure, an account is free but might require giving information you don't want to give. Twitter asks…
that's what old.reddit.com is for!