I haven't used a public site since Suprnova so I don't know about the health of public p2p sites at all. The private side is absolutely not stagnant, new sites pop up all the time and you can still find all the niche stuff you want to find by just nudging the enthusiasts with requests.

A lot of them seed from home, with humongous servers, and there are preservation programs going on in various places.

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.