It's because they put the personal information of Imgur administrators in the sidebars and encouraged people to investigate/harass them.
It turns out that when you break the rules you get banned. Surprising, right?
also, lol, free speech on a private website - "they're infringing on my right to harass people! what a travesty!"
Then why does /r/stuffRedditSays and /r/SubredditDrama exist?
Those two literally have investigateed, brigaded, and harrassed, yet they dodge the People's Banhammer of Ellen Pao
Whatever, at least Reddit can be put out of its misery and stop being relevant, like what happened to digg.
I hope next up is the destruction of Tumblr.