No, quite the opposite. Nearly every router has a very simple option to not allow packets from IPs not on the same CIDR as the interface. If ISPs turned this on on each edge interface, the problem would be solved.

It's entirely political/economic. There is no incentive for an ISP to do so because it provides no direct benefit. It's a classic issue of externalities.

It's also worse, because if you were to deploy BCP38, you don't really get a whole lot from it. Sure, it's a good thing to do, but at the end of the day people aren't going to pick your service because you have BCP38 setup properly.