Unfortunately, there's no convenient global IP-to-email or IP-to-person database, so it's not as easy as you may think to contact those affected. IPs are usually dynamically assigned to consumer users, meaning there's no simple one-to-one mapping. While it's certainly *possible* to track down a user by IP, it's by no means trivial to do so, or even possible in all cases. ISPs may be reluctant to hand out that information to law enforcement without a subpoena, and that's generally a good thing for our privacy.
Probably the most effective response to help individuals, now that the authorities have the command and control systems, is to instruct the malware to remotely disable itself and patch any known infection vector / vulnerability. This has been done on several occasions by the FBI and Microsoft in recent years, which has a dedicated anti cyber-crime lab that works with them on these sorts of cases. Of course, this is fraught with both technical and legal concerns, due to potential abuse or a slippery slope encroachment of privacy rights. And things are made more complicated because of the various international laws that may impact the ability of law enforcement to do this.
I certainly understand your skepticism regarding governments, law enforcement, and potential for abuse by overreach, but I really do think they're doing the right thing here. It's unfortunate that governments and law enforcement has undermined the public trust with their actions, such that we can't help but question their motivations, even when they're (I believe) legitimately stopping criminals like this.