[Retric]

Many ISP’s have significantly more and largely unused bandwidth between users vs the overall network. This is often done for simple redundancy as you want a minimum of two upload links if not more. However, it’s much simpler to run a wire between two different tiny grey buildings in a neighborhood than run a much longer wire to another section of your core network. Ideally that’s just a backup for your backup, but properly configured routers will still use it for local traffic.

Another common case is if you want X bandwidth from A to B you round up to hardware with some number more than X. This can result in network topology’s that seem very odd on the surface.

PS: I think you’re confusing what I am saying, this is not pure P2P it’s very much a hybrid model. Further Netflix was seriously considering it for a while in 2014, but stuck with a simpler model.