There's a few reason's for that...Gone but not forgotten. Shame it didn't have the traction to build like 8chan did.
- Once 8kun opened it's doors, majority of 8ch refugees flocked to that, even with the warning signs that things were not going to be the same as before, learning absolutely nothing from the 4chan Exodus years ago when GamerGate was a thing. Getting them to move out of their "comfort zone" is a futile effort and they are now no better than the normalfags on 4chan.
- Too many bunkers started to open up, especially ones dedicated to specific sub-categories (eg. Julay with a high-priority on /cow/, Vch with a high-priority on /v/, etc...), creating a divide with people that still enjoyed image boards
- Even with advertisement, you still had people advertising other boards within 9chan that were "supposedly better"