They don't. Hawking radiation doesn't come from inside the event horizon. I am trying to paraphrase Matt O'Dowd here, but the short short version as I understand, an event horizon causes certain frequencies in quantum fields to no longer cancel. The effect is that, for an observer far away from the black hole, the black hole emits radiation. The energy comes from the mass of the black hole, I don't think anyone really knows how that happens since we don't really know what a black holexs mass is made of (if anything),