From what I understand they don't necessarily target torrent sites directly, although they don't particularly want to be associated with them either. The main reason trackers have been coming to the fore and being targeted recently, and someone correct me if I'm wrong, is due to the high number of disputes put into paypal linked with the accounts used by the trackers.
A lot of these disputes, although not entirely limited to, come from traders donating to get invites, getting the invites then 'claiming' their money back from paypal...
I know this is gonna open up a huge can of worms again... "Traders are scum of the earth" Vs "Trackers shouldn't offer invites for donations"... but who cares...
As far as I understand it, that's what the recent problems have been caused by...