alt Hacker NewsYes, that's true, but the core reason there are private p2p sites is because you're most likely to get a DMCA violation letter from the watchdog company via your ISP or to you directly in the West.
Even if it may be not a punishable offense, that still freaks out people, and they choose not to seed from home or use public websites which are scraped by DMCA watchdogs.
I don't see much point in contributing to closed silos (even if I'm present on the majority of invite-only music trackers and occasionally contribute there) because I have ThePirateBay and RuTracker account: it's the same, but it's open for everyone and google-able.
Some private trackers disallow accessing them via VPN, which I find super strange. They want to access the website with your residential connection, but they allow seeding via VPN (which many do, because see above).
Other private tracker which I used to be on had a timeout on account life time. If you don't log in once in a while (6 months AFAIR), your account will be suspended, even if you're seeding all the content in the torrent client all this time.
I think for normal people, private trackers seem inaccessible and might as well not exist. When I was a kid, I had gobs of free time and spent most of it dialing into BBS systems, learning who to contact, and navigating the scene's trust network, just to get invites to warez sites. Now that I'm an adult, I'm a lame Casual, too busy living my life to have time to sit there figuring out the secret handshake needed to get an invite to Private Tracker X.