I never understood this, is there anything that makes it difficult for the original uploader, the one that supposedly offers the file directly, to offer a torrent instead for the same amount of time?
As far as perennity is concerned it seems strictly better.
If they're no longer using that model they may not be willing to continue using their storage for it.
You can add an existing HTTP download as a "web seed" to a torrent, so they don't actually need to do anything for people to share it as a torrent.
Every change to the source is effectively a new torrent. This creates a ton of fragmentation as data is reorganized, remixed, reencoded, and so on.
You can see this with many Linux distros: there is no single Debian torrent that people seed for years because there's always a refreshed version.
Distros are a bad use case for P2P anyway since you depend on upstream as soon as you start upgrading and installing packages.