Because it's a game.

[Although he's not laughing at her anymore, the corner of his mouth does quirk up, wryly amused.]

If I want to take someone's money, they'll never know I was anywhere near them. If I take something, let myself be seen, then the other person gets to play the game, too. It's an invitation. "Step inside the circle and see how it's done." That's all. Sometimes people choose to accept that invitation, sometimes they don't.