Unlike public trackers, private trackers are largely filled with seeders with very few leechers. If 50 people have a file and one person goes to download you are only getting a tiny slice of that at best and for small files there may not even be enough chunks to get anything at all.

It makes no sense to me since bandwidth is so cheap compared to 20+ years ago and I think the incentives should instead encourage variety and availability like a distributed, highly-available, P2P archive.