All of these platforms are still used by many. As a someone who left Reddit for Lemmy I gotta say a lot of these people have a heavy dose of copium saying Reddit is dead just because they'd like it to be.
When I think of it as dead I think of it the same way as Facebook. Sure it's still there but the vibe is thoroughly dead. They're where people get comfy and retire to stay stuck in their ways while others move on to greener pastures.
These platflorms are all declining. Facebook has been for years. This path leads to certain death. There is no way for them to recover from their past mistakes. So it's equivalent to being already dead for me
I like to think of them as retirement homes. Boomers retired on Facebook. The next gen of boomers will now retire on Reddit. I hope I never retire anywhere I want to try all the new things forever :(