It's called "Civil Asset Forfeiture" and it has become very controversial. In general, the government (i.e. - local/state police, FBI) can immediately seize assets from suspected illegal activity (typically drugs). For example, if a person is seen leaving a drug-lord's hideout with a duffel bag full of cash, they can seize the money to help stop the illegal activity. In that regard it has been very successful.
The kicker is this - the person carrying the cash doesn't have to break any laws to have the money seized. Just the suspicion is sufficient. And, once the money is seized, the owner has to prove the money was 'innocent' before getting it back. People have the protection of 'innocent until proven guilty', but property (i.e. - cash) does not.
Because of this, some unscrupulous police have taken to seizing any large quantities of cash found in ordinary traffic stops on the belief that anyone carrying that much cash is up to no good in some way. And, if uncontested, they get to keep the cash, thus providing a great incentive to continue the behavior.
Sounds like piracy to me