Alternative explanation: when trying to solve a problem attack the biggest issue first. If TPB was the torrent site for a majority of users (and especially for casual users) then you attack that site first. Now that it is down you move on to #2, #3, etc. The niche sites are less important than the mega-site, but that does not mean that they are not on someone's radar or not going to be next on the list. The "why go after me when TPB is out there doing much worse to you" excuse also goes away.