A few months ago I grabbed this torrent from rarbg, and it took weeks to download. Often going days with no seeders.
I finally got it, and decided I'd seed beyond my usual 2x to help others get this. Then rarbg went under, and now I think I'll just keep this one going.
They do, but if you can't forward a port nothing can get to you from outside, which you want with P2P, per default anything from outside is blocked.
If two people with no port forwarding meet, they aren't able to connect, one side has to have an open port, so you're missing many peers and seeders and you can counter this by being the one with the open port so anyone is able to connect to you.