Why is the BMW 4 Series known for its impressive fuel efficiency?

I've been hearing a lot about the BMW 4 Series and how it's known for its impressive fuel efficiency. Can you explain why this is the case?

The BMW 4 Series utilizes advanced aerodynamics, lightweight construction, and efficient engines, all contributing to its impressive fuel efficiency.

The start/stop system in the BMW 4 Series automatically shuts off the engine when you come to a stop, saving fuel in city traffic.

I've found that driving in Eco Pro mode greatly improves fuel efficiency. It's a great feature to use when you're in heavy traffic or on long drives.