Once it gets too big the chance to get away with it gets really slim. If you steal some millions you can dissapear and If you aren't too stupid no one will find you and after a while everyone will forget you.
But with hundreds of millions you won't bei forgotten and the agencies will put enough manpower in finding you.
Yeah, it seems the key is in exploiting the lack of law enforcement resources. I read an article yesterday about Canadian doctors trafficking fentanyl patches. The,now retired, agent who busted a small ring said he could have gotten 1000 doctors if he had the resources. He also mentioned the courts would not back him up on a large bust either. If he brought them 100 doctors he said they would tell him to pick the worst seven.