I think you can reasonably blame the lack of features here, honestly. I'm not saying if they had them they would have challenged Reddit, but they'd have been much more active. Community moderators almost certainly lost interest when they realised they had no real control over their community, and the longer the time elapsed with no tools to do so - the more drifted away leaving abandoned communities where AI and bots and trolls move in - compounding it even further.

They also, on day 1 of their community launch, allowed day 1 old accounts to make communities. Even if each account could only moderate 2 communities, that wasn't smart at all.