>I always thought you are supposed to set up an old PC yourself.
You can do that as well of course. I just find a seedbox more comfortable as I don't have to worry about electricity prices, it's faster, dedicated hardware resources and more storage than I currently have at home.
>Don't VPSes usually forbid using torrents? At least the cheap ones for sure.
There are seedbox providers specialized on torrenting (feralhosting, seedhost, hostingby.design, whatbox.ca for example). But I used an OVH VPS once for torrenting and they didn't forbid anything, Hetzner allowed it as well.