I wish I shared your optimism with the legal system, but it seems that years of stacking the courts with pro-police-state judges has led to many of these kind of cases ending in favor of governmental overreach.

This is really just laziness on the part of the feds. Instead of doing the actual work involved to find out if infringement is happening, they just lazily seize the domains they're allowed to seize (those registered in the US) and wait for the owners of the site to complain. The real infringers will just register a new domain with a foreign registrar, while the innocent people will almost never have the resources to fight back.

I don't know whether the sites in question were doing anything illegal, and neither does DHS/ICE. It's despicable that presumption of innocence is sacrificed so the RIAA can gain a few more scalps.