Wow I never heard of AV1 before, it sounds really promising!

For me:

• Lifetime of torrents, honestly I rarely have dead torrents on private trackers. Also, most of them send an alert to previous seeders telling them one torrent needs some seeds. So for that it's WAY better than public.
• Niche contents, I'm into rare movies and some movies are only available on private trackers (unfortunately), so yeah, for me no choice. Though I really miss VXT releases on RARBG :(.

Except that.. Not much. I think I still would keep my seedbox if I was on public trackers. Private or public, we all have to do our jobs and participate in seeding what we got :)

This really depends... I'm on a lot of private trackers but I miss RARBG more and more. Just for their x265 (that is usually absent on private trackers) and even more their VXT-265.