There is something to be said about StackOverflow perennial content idea, but maybe something already said it better.

Twitter seems to be the enigma to that rule, because I still get heated replies to tweets from years ago from time to time. Even though time has passed, the conversation is still as shallow as ever.

I can't imagine being a celebrity and getting dozens of hate tweets in my mentions because a tweet I made 8 years ago shows up as a link on a facebook group somewhere.

Well, they lock threads after 6 months, probably to save moderation time. It's always possible for someone to re-create a discussion topic and get new responses going.