Basically, amazing initial design, and fly by wire. The B2's shape is the result of the most advanced computer aided design available at the time. It's an optimized shape for stealth, stability, and efficiency. There are also so many minute stabilization inputs happening in the back ground by the flight hardware/software.

It's wide and can have drag on either wing edge, it's center of thrust is tucked very close to the center, so little inputs from the control surfaces on the extremities can impart quite a bit of influence on the plane as a whole.

Also, they're mission plans and performance envelope avoid a ton of atmospheric fuckery. Whether it's waiting for the weather to clear, flying above it, or aerial refueling to fly around it. They see clean air.