because torrents are very difficult to track even if the ISP knows who did it, they can't give it to third parties without a arrest warrent.
ISP would probably give out a warning like disconnecting their service due to violation with ToS. Howevere, it rarely happens and bittorrents are known to be extremely covert and much difficult to track.. so it's useless, and governments doesn't care; RIAA and MPAA does.