They force you to create accounts and hand over personal info that can get you busted later when the site gets raided, or just silently handed off to the authorities who run it themselves for a time collecting data to go after the pirates later. Now they've got logs of your username, possibly your password, the email address you signed up with, and lists of every IP addresses you've used and when, interview questions/answers, detailed records of every single file you've ever downloaded/shared. It's gotten people caught many times.
A tracker/website shouldn't know anything about you other than the IP address of the VPN you're using (which should change every single time you connect) and whatever information they can collect from your BitTorrent client and the locked down dedicated browser you're using whose fingerprint should also change regularly. No logins/accounts. No need to have your download/IP address history tracked and tied to anything that could point back to you. Ideally the site you use shouldn't even know what files you're downloading since you should be able to simply copy the magnet link instead of clicking on the names of the files you want or downloading torrent files from the server.