That’s why torrents get faster as more people download, it’s asymmetrical downloading. So imagine a Lego set and everyone has a few pieces and they can copy those pieces and tell the other people where they go.

More people means the set gets done faster and no one needs the whole original file, just a set of instructions on how to assemble it.

You use a seedbox because trackers keep track of your ratio (on average there have to be as many of more uploaders as downloaders or it stops working). On private trackers with smaller user bases, you need to enforce seeding unjustly by giving people who seed heavily some sort of reward (higher download limit, flair, access to a special chat, etc).