Yes, 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.