I kind of agree, but the way the internet is going, with everyone being behind carrier-grade nat, it's not much of a decentralized network of computers anymore, not to mention all the kids with their laptops and tablets not even hosting anything :(
UPnP is just automating the process of forwarding ports, CGNAT will still screw you sideways because you're behind a router you can't access or order around.
There are ways around this, I've experimented with setting up a cluster of ArchiveBox instances that share snapshots over Tailscale. Tailscale lets users sign up for free accounts, and you can share machines between separate accounts. A (CGNAT-compatible) decentralized invite-only network could concievably spread that way.