Crimes are brought by the government once it discovers the crime, not by anyone. Anyone can provide evidence to the government that a crime was committed.
Correct. Now please picture me how your wife's kidnapper goes to the police saying that the ransom you paid exceeded $10k.
Someone who did a much more serious crime is not gonna go to law enforcement because his ass is going to be the one charged considering the circumstances.
But if a massive cash transaction is illegal good luck kidnapper doing stuff with a bulk of ransom money. Hey it may even put him off that whole kidnapping idea yeah? Or at least get him caught so he doesn't kidnap more people somewhere else