Of course its not the same. What ever is after over a decade?
It's a forum. People come and go. Once staple posters get busy with real life, new people come in, big events draw in crowds, dull periods see the casual audience shift away, Naruto and Bleach both end so we can't make fun of those the same way anymore… things change. That's life. You go to ANY forum based around an ongoing series and that's going to happen... Go compare the activity on a Gargoyles forum in 1998 to its activity in 2004, then compare that to it's activity now. it's just rare that you find a series that actually runs for the length of a lifetime that has something new to actually talk about week after week.
One Piece is almost 22 years old (older than some of the people on the forum!) and a daunting nearly 100 volumes/850 episodes long, and it's still got probably another decade to go, and the worldwide community is caught up with it. It's going to be hard pressed for it to ever be as active and fresh or drawing in as many new people on a regular basis as it once did, because its not new anymore, and what is there is a scary amount of backlog for someone to jump into fresh.
Also, as far as forum traffic, there is a difference between not caring about traffic from lurkers who never post and contribute, and , caring about the active community. They are different things. I do care about the later.