It’s a lot easier to find out who is torrenting than to find out who is using Usenet for example though.
With torrents you can see the IP addresses of peers. And then I suppose they ask a court to tell the ISP to say which customer had that IP addresses at that time.
With Usenet you’d have to get a court to get each Usenet provider to give you a list of all customers that downloaded a file. That seems a little bit different to me.
And who knows, in the case of the torrents maybe they don’t always even need to get a court involved. With all of the data brokers out there, maybe there are lists you can buy of real people tied to different IP addresses and when you have a match you send a threatening letter telling them to pay up or they will take you to court?