Two things:

1) You're saying this because you're intelligent. But because you're intelligent, you're also less likely to turn to a life of crime. You can make money honestly and you have a lot to lose if you get busted. Crooks tend to be uneducated and ignorant.

2) It's easy to keep a secret that only you know. But there's usually more than one person involved in a crime. Are all of your companions in crime going to be as careful? People just can't resist talking. They want to brag. They want to tell their friends and loved ones. And as time goes on, people let their guard down.