I've always had trouble defineing the difference between a website that is slow like 4-ch or tgchan, and a website that is dead like 99chan or 7chan
I feel like the unity of the community has a lot to do with it. 4-ch has a "core" group of dedicated users as well as a style of posting that is specific to itself. The threads all feel like they're a part of something greater; as if they were all connected in some way
7chan, whilst it gets more traffic, has no core userbase that consistently returns to it. All of the threads exist in a vacuum, and there's no specific flavor to the content