If the majority of ASNs in the world followed BCP 38, these attacks would be more difficult because the origin would be easily identifiable. Today you can't tell where it's coming from because backwater networks see value in letting their customers emit forged packets however they like. So all you can do is mitigate and wait for them to move on.

BCP 38/RFC 2827 would change the DoS game, but it's been a best practice for longer than most of this audience has been alive and nobody yet gives a shit and/or they are too lazy to automate the implementation. So operators waste their lives cleaning up after bad actor ASNs that they can't even identify. I shouldn't be mitigating 65 Gbps destined for a controversial customer, the attacker should be removed from the Internet before I even notice.

You can tell from my tone that attacks are part of life for me. I'd venture that denials are the second largest problem facing the Internet today, behind the organizational structure of critical systems like DNS and ahead of spam and surveillance. However, there is now a sizable DoS prevention industry so I wouldn't be surprised if BCP 38 drifts into even more obscurity, but that's the cynic typing.