[kelnos]

I think for the most part because it's not needed. Anything hosted on a .com, .net, .org (or any other TLD where the TLD's root DNS is managed by a US company) can be taken down with a court order. There's no need to involve ISPs.

In general they're not going to bother with IP blocking; once they've killed DNS, they're satisfied that most people will not be able to access it.

And for the most part, that's good enough. There's perhaps an argument that the US gov't should be blocking IPs/DNS of things like hacking rings and malware distributors that are hosted elsewhere, on TLDs out of their reach (where ISP blocking would probably be the only or at least best way), but they mainly only care about e.g. sites that threaten the copyright cartels, when it comes to legal takedowns, anyway. And for sites that host illegal content, they seem happy only prosecuting US residents who access them.