This is the negative of private invite-only trackers like what.cd. If they end up closing a lot of data gets dies with them. In contrast to that piratebay and nyaa.pantsu regularly upload their databases and there are even offline database readers for them.
Years ago, I was on a university private tracker. It was used more to share hard-to-find resources than for any actual piracy, much less piracy of anything new or policed. (I'm sure people stole plenty of 50-year-old textbook PDFs.) But when the hoster shut it down abruptly, everything simply vanished, including all kinds of hand-scanned and annotated stuff which may be literally irreplaceable.
Meanwhile, something like Kickass Torrents can be shut down and abandoned by the owners, but the content all reappears almost immediately. The private-tracker model has lots of advantages for community building, but as far as robustness it undermines the entire concept of P2P sharing.
