Why couldn't the Concorde cruise lower?

The Concorde could not cruise at lower altitudes primarily due to its design and the physics of supersonic flight. At lower altitudes, the aircraft would encounter increased air resistance and drag, making it less efficient and unable to maintain supersonic speeds. Additionally, operating at lower altitudes would violate noise regulations in many regions due to the sonic boom created during supersonic flight. Thus, cruising at high altitudes allowed the Concorde to optimize its performance and comply with regulatory constraints.