The activity of NB was halved when Madara got blitzed by Black Zetsu. That chapter enraged the Naruto fandom.
At this point AB has outlasted many competing forums. Even if activity is not the best, there is assurance of long term forum support.
Many people including me have complained that the current theme is too bright. I think it makes the theme look unappealing. If they have a dark theme with the same layout it will look ten times better.