I mean they aren't really that dead, people usually talk in each of the forums every day (or once every few days). The most active forums are by far The Site and Introductions, but every so often Talk can get going pretty good too.
In general though, the site wide forums aren't super duper active because most people I'm sure spend most of their time talking in game forums or external places like Discord servers. Most of the chatter here in the main stuff is for questions/answers and whatnot.
What are your expectations? Hundreds of posts a day?
Allot of talk is kept in the community, since not everyone asks questions regarding a game in the general forums ... except for some heroes -.- To see what's going on you should keep an eye on the game's forums if you care about that. But since discord becomes more of a thing, allot of communities "abandon" the regular forums for normal talk since it's easier and faster.
Just because not everyone is having permanent issues on how to start Livesplit or because usually the most people can use a damn search engine, it's simply not flooded with dumb and the same questions over and over again which I think is good.
As previously mentioned, it's moreso the fact that social interaction in speedrunning communities tends to take place in, well, the actual sub-communities. There's this huge misconception that speedrunning is one big community, and it really isn't. Obviously there is overlap between communities on an individual level, but by and large the speedrunning communities are defined on a game-by-game/series-by-series basis, so the main hubs for social interaction are places like individual game forums or Discord servers. Just checked the Sonic Speedrunning Discord to try and prove that point, and yeah. Since last night, absolutely tons of new messages including strat talk, visual cues for tricks, people showing their new PBs, etc. You won't find any of that on the SRcom forums for the Sonic games.
So in other words, if there's a particular game you play, find out where the community hangs out and go there, likely a Discord server.
Not saying I don't like this, it's actually nice to see such a friendly and quite community. Still trying to figure out what to speedrun...