The middle (ntt, gtt, tata, etc) of the internet doesn't know what is or isn't spoofed. The folks at the edge own that responsibility and most colo/hosting shops allow their customers to spoof. Their upstreams are powerless against them since they'll take their money elsewhere.
Not talking about peering. Talking about transit-customer relationships. Think large hosting shops who say they can't afford to do uRPF on their customers because they've got so many multihomed users and the IP address space is fluid. Or smaller regional networks selling low cost transit. Some folks just have arbitrary limits (you must have x asns behind you for us to remove urpf)
