I've seen this discussed elsewhere. It seems the US government is well aware of the ISP and these sites and has made the strategic decision to let them stay up and running in order to gather intel from them. There are serious questions as to whether that's a good idea, but I think that's what's going on.
Referencing my post above, Internet Haganah has been unveiling these sites (and their ISPs) for years. In many cases the ISPs shut them down, and in others they simply “disappear” or become unusable and disabled.
A couple years ago there was a lengthy and well-publicized battle between Internet Haganah and certain federal agencies on the question of public disclosure.
Yes and please see my post # 6 on why I am absolutely convinced that it is a horrible idea to keep these terrorist forums/websites operating.